Network Working Group P. Saint-Andre
Internet-Draft Cisco
Obsoletes: 3921 (if approved) March 31, 2010
Intended status: Standards Track
Expires: October 2, 2010
Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and
Presence
draft-ietf-xmpp-3921bis-06
Abstract
This document defines extensions to core features of the Extensible
Messaging and Presence Protocol (XMPP) that provide basic instant
messaging (IM) and presence functionality in conformance with RFC2779.
This document obsoletes RFC 3921.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on October 2, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
Saint-Andre Expires October 2, 2010 [Page 1]

Internet-Draft XMPP IM March 20101. Introduction1.1. Overview
The Extensible Messaging and Presence Protocol (XMPP) is an
application profile of the Extensible Markup Language [XML] for
streaming XML data in close to real time between any two (or more)
network-aware entities. XMPP is typically used to exchange messages,
share presence information, and engage in structured request-response
interactions. The core features of XMPP defined in [XMPP-CORE]
provide the building blocks for many types of near-real-time
applications, which can be layered on top of the core by sending
application-specific data qualified by particular XML namespaces
(refer to [XML-NAMES]). This document defines XMPP extensions that
provide the basic functionality expected of an instant messaging (IM)
and presence application as defined in [IMP-REQS].
As a result of extensive implementation and deployment experience
with XMPP since 2004, as well as more formal interoperability testing
carried out under the auspices of the XMPP Standards Foundation
(XSF), this document reflects consensus from the XMPP developer
community regarding XMPP's basic instant messaging and presence
features. In particular, this document incorporates the following
backward-compatible changes from RFC 3921:
o Incorporated corrections and errata
o Added examples throughout
o Clarified and more completely specified matters that were
underspecified
o Removed the protocol for session establishment, which was deemed
unnecessary
o Modified error handling related to presence stanzas to more
seamlessly repair lack of synchronization in subscription states
between rosters located at different servers
o Added optional server support for pre-approved presence
subscriptions
o Added optional 'parent' attribute to <thread/> element
o Transferred documentation for the communications blocking protocol
from this specification to a separate specification
Therefore, this document defines the basic instant messaging and
presence features of XMPP 1.0, thus obsoleting RFC 3921.
1.2. Requirements
Traditionally, instant messaging applications have combined the
following factors:
Saint-Andre Expires October 2, 2010 [Page 6]

Internet-Draft XMPP IM March 2010
1. The central point of focus is a list of one's contacts or
"buddies" (in XMPP this list is called a ROSTER).
2. The purpose of using such an application is to exchange
relatively brief text messages with particular contacts in close
to real time -- often relatively large numbers of such messages
in rapid succession, in the form of a one-to-one CHAT SESSION as
described under Section 5.1.
3. The catalyst for exchanging messages is PRESENCE -- i.e.,
information about the network availability of particular contacts
(thus knowing who is online and available for a one-to-one chat
session).
4. Presence information is provided only to contacts that one has
authorized by means of an explicit agreement called a PRESENCE
SUBSCRIPTION.
Thus at a high level this document assumes that a user must be able
to complete the following use cases:
o Manage items in one's contact list
o Exchange messages with one's contacts
o Exchange presence information with one's contacts
o Manage presence subscriptions to and from one's contacts
Detailed definitions of these functionality areas are contained in
RFC 2779 [IMP-REQS], and the interested reader is referred to that
document regarding the requirements addressed herein. While the XMPP
instant messaging and presence extensions specified herein meet the
requirements of RFC 2779, they were not designed explicitly with that
specification in mind, since the base protocol evolved through an
open development process within the Jabber open-source community
before RFC 2779 was written. Although XMPP protocol extensions
addressing many other functionality areas have been defined in the
XMPP Standards Foundation's XEP series (e.g., multi-user text chat as
specified in [XEP-0045]), such extensions are not specified in this
document because they are not mandated by RFC 2779.
Note: RFC 2779 stipulates that presence services must be separable
from instant messaging services and vice-versa; i.e., it must be
possible to use the protocol to provide a presence service, an
instant messaging service, or both. Although the text of this
document assumes that implementations and deployments will want to
offer a unified instant messaging and presence service, there is
no requirement that a service must offer both a presence service
and an instant messaging service, and the protocol makes it
possible to offer separate and distinct services for presence and
for instant messaging. (For example, a presence-only service
could return a <service-unavailable/> stanza error if a client
attempt to send a <message/> stanza.)
Saint-Andre Expires October 2, 2010 [Page 7]

Internet-Draft XMPP IM March 20101.3. Functional Summary
This non-normative section provides a developer-friendly, functional
summary of XMPP-based instant messaging and presence features;
consult the sections that follow for a normative definition of these
features.
[XMPP-CORE] specifies how an XMPP client connects to an XMPP server.
In particular, it specifies the preconditions that must be fulfilled
before a client is allowed to send XML stanzas (the basic unit of
meaning in XMPP) to other entities on an XMPP network. These
preconditions comprise negotiation of the XML stream and include XML
stream establishment, optional channel encryption via Transport Layer
Security [TLS], mandatory authentication via Simple Authentication
and Security Layer [SASL], and binding of a resource to the stream
for client addressing. The reader is referred to [XMPP-CORE] for
details regarding these preconditions, and knowledge of [XMPP-CORE]
is assumed herein.
Note: [RFC3921] specified one additional precondition: formal
establishment of an instant messaging and presence session.
Implementation and deployment experience has shown that this
additional step is unnecessary. However, for backward
compatibility an implementation SHOULD still offer that feature
and note in the stream feature that negotiation of the feature is
discretionary (via the <optional/> child element). This enables
older software to connect while saving newer software to skip a
round trip.
Upon fulfillment of the preconditions specified in [XMPP-CORE], an
XMPP client has a long-lived XML stream with an XMPP server, which
enables the user controlling that client to send and receive a
potentially unlimited number of XML stanzas over the stream. Such a
stream can be used to exchange messages, share presence information,
and engage in structured request-response interactions in close to
real time. After negotiation of the XML stream, the typical flow for
an instant messaging and presence session is as follows:
1. Retrieve one's roster. (See Section 2.2.)
2. Send initial presence to the server for broadcasting to all
subscribed contacts, thus "going online" from the perspective of
XMPP communication. (See Section 4.2.)
3. Exchange messages, manage presence subscriptions, perform roster
updates, and in general process and generate other XML stanzas
with particular semantics throughout the life of the session.
(See Section 5, Section 3, Section 2, and Section 6.)
Saint-Andre Expires October 2, 2010 [Page 8]

Internet-Draft XMPP IM March 2010
4. Terminate the session when desired by sending unavailable
presence and closing the underlying XML stream. (See
Section 4.5.)
1.4. Conventions
This document inherits the terminology defined in [XMPP-CORE].
The following keywords are to be interpreted as described in [TERMS]:
"MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD",
"RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
For convenience, this document employs the term "user" to refer to
the owner of an XMPP account; however, account owners need not be
human persons and can be bots, devices, or other non-human
applications.
Following the "XML Notation" used in [IRI] to represent characters
that cannot be rendered in ASCII-only documents, some examples in
this document use the form "&#x...." as a notational device to
represent Unicode characters (e.g., the string "&#x0159;" stands for
the Unicode character LATIN SMALL LETTER R WITH CARON).
In examples, lines have been wrapped for improved readability,
"[...]" means elision, and the following prepended strings are used
(these prepended strings are not to be sent over the wire):
o C: = client
o CC: = contact's client
o CS: = contact's server
o S: = server
o UC: = user's client
o US: = user's server
1.5. Acknowledgements
The editor of this document finds it impossible to appropriately
acknowledge the many individuals who have provided comments regarding
the protocols defined herein. However, thanks are due to those who
have who have provided implementation feedback, bug reports, requests
for clarification, and suggestions for improvement since the
publication of the RFC this document supersedes. The editor has
endeavored to address all such feedback, but is solely responsible
for any remaining errors and ambiguities.
Portions of the text about roster versioning has been borrowed from
[XEP-0237].
Saint-Andre Expires October 2, 2010 [Page 9]

Internet-Draft XMPP IM March 20101.6. Discussion Venue
[[ RFC Editor: please remove this section. ]]
The document editor and the broader XMPP developer community welcome
discussion and comments related to the topics presented in this
document. The primary and preferred venue is the <xmpp@ietf.org>
mailing list, for which archives and subscription information are
available at <https://www.ietf.org/mailman/listinfo/xmpp>. Related
discussions often occur on the <standards@xmpp.org> mailing list, for
which archives and subscription information are available at
<http://mail.jabber.org/mailman/listinfo/standards>.
2. Managing the Roster
In XMPP, one's roster contains any number of specific contacts. A
user's roster is stored by the user's server on the user's behalf so
that the user can access roster information from any resource.
Because the user's roster can contain confidential data, the server
MUST restrict access to this data so that only authorized entities
(typically limited to the account owner) are able to retrieve,
modify, or delete it.
2.1. Syntax and Semantics
Rosters are managed using IQ stanzas, specifically by means of a
<query/> child element qualified by the 'jabber:iq:roster' namespace.
The detailed syntax and semantics are defined in the following
sections.
2.1.1. Ver Attribute
The 'ver' attribute is a string that identifies a particular version
of the roster information. The value MUST be generated only by the
server and MUST be treated by the client as opaque. The server can
use any appropriate method for generating the version ID, such as a
hash of the roster data or a strictly-increasing sequence number.
Inclusion of the 'ver' attribute is RECOMMENDED.
Use of the 'ver' attribute is described more fully under Section 2.6.
2.1.2. Roster Items
The <query/> element MAY contain one or more <item/> children, each
describing a unique ROSTER ITEM or "contact".
Saint-Andre Expires October 2, 2010 [Page 10]

Internet-Draft XMPP IM March 2010
The syntax of the <item/> element is described in the following
sections.
2.1.2.1. Ask Attribute
The 'ask' attribute is used to specify certain subscription sub-
states; for details, see Section 3.1.2.
Inclusion of the 'ask' attribute is OPTIONAL.
2.1.2.2. Jid Attribute
The 'jid' attribute specifies the Jabber Identifier (JID) that
uniquely identifies the roster item.
Inclusion of the 'jid' attribute is REQUIRED.
2.1.2.3. Name Attribute
The 'name' attribute specifies the "handle" to be associated with the
JID, as determined by the user (not the contact). Although the value
of the 'name' attribute MAY have meaning to a human user, it is
opaque to the server. However, the 'name' attribute MAY be used by
the server for matching purposes within the context of various XMPP
extensions, in which case the values MUST be compared only after
application of the Resourceprep profile of stringprep as defined in
[XMPP-CORE].
Inclusion of the 'name' attribute is OPTIONAL.
2.1.2.4. Subscription Attribute
The 'subscription' attribute is OPTIONAL; see Section 2.1.7.
Inclusion of the 'subscription' attribute is OPTIONAL.
2.1.2.5. Group Element
The <group/> child element specifies a category or "bucket" into
which the roster item is to be grouped by a client. An <item/>
element MAY contain more than one <group/> element, so that roster
groups are not exclusive. Although the XML character data of the
<group/> element MAY have meaning to a human user, it is opaque to
the server. However, the <group/> element MAY be used by the server
for matching purposes within the context of various XMPP extensions,
in which case the data MUST be compared only after application of the
Resourceprep profile of stringprep as defined in [XMPP-CORE].
Saint-Andre Expires October 2, 2010 [Page 11]

Internet-Draft XMPP IM March 2010
Inclusion of the <group/> child element is OPTIONAL.
2.1.3. Roster Get
A ROSTER GET is a client's request for the server to send the roster;
syntactically it is an IQ stanza of type "get" sent from client to
server and containing a <query/> element qualified by the 'jabber:iq:
roster' namespace, where the <query/> element MUST NOT contain any
<item/> child elements.
C: <iq from='juliet@example.com/balcony'
id='rg1'
type='get'>
<query xmlns='jabber:iq:roster'/>
</iq>
The expected outcome of sending a roster get is for the server to
return a roster result.
2.1.4. Roster Set
A ROSTER SET is a client's request for the server to modify (i.e.,
create, update, or delete) a roster item; syntactically it is an IQ
stanza of type "set" sent from client to server and containing a
<query/> element qualified by the 'jabber:iq:roster' namespace.
The following rules apply to roster sets:
1. The <query/> element MUST contain one and only one <item/>
element.
2. The server MUST ignore any value of the 'subscription' attribute
other than "remove" (see Section 2.1.7).
3. The server MUST ignore any 'to' address specified on the IQ
stanza and MUST handle the IQ stanza as if it included no 'to'
attribute.
C: <iq from='juliet@example.com/balcony'
id='rs1'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'/>
</query>
</iq>
Saint-Andre Expires October 2, 2010 [Page 12]

Internet-Draft XMPP IM March 20102.1.5. Roster Push
A ROSTER PUSH is a newly created, updated, or deleted roster item
that is sent from the server to the client; syntactically it is an IQ
stanza of type "set" sent from server to client and containing a
<query/> element qualified by the 'jabber:iq:roster' namespace.
The following rules apply to roster pushes:
1. The <query/> element in a roster push MUST contain one and only
one <item/> element.
2. A receiving client MUST ignore the stanza unless it has no 'from'
attribute (i.e., implicitly from the user's bare JID) or it has a
'from' attribute whose value matches the user's bare JID
<user@domain>.
S: <iq id='a78b4q6ha463'
to='juliet@example.com/chamber'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'/>
</query>
</iq>
As mandated by the semantics of the IQ stanza as defined in
[XMPP-CORE], each resource that receives a roster push MUST reply
with an IQ stanza of type "result" (or "error").
C: <iq from='juliet@example.com/balcony'
id='a78b4q6ha463'
type='result'/>
C: <iq from='juliet@example.com/chamber'
id='a78b4q6ha463'
type='result'/>
Note: There is no error case for client processing of roster
pushes; if the server receives an IQ of type "error" in response
to a roster push it SHOULD ignore the error.
2.1.6. Roster Result
A ROSTER RESULT is the server's response to a roster get;
syntactically it is an IQ stanza of type "result" sent from server to
client and containing a <query/> element qualified by the 'jabber:iq:
roster' namespace.
The <query/> element in a roster result contains one <item/> element
Saint-Andre Expires October 2, 2010 [Page 13]

Internet-Draft XMPP IM March 2010
for each contact and therefore can contain more than one <item/>
element.
S: <iq id='rg1'
to='juliet@example.com/chamber'
type='result'>
<query xmlns='jabber:iq:roster' ver='ver7'>
<item jid='nurse@example.com'/>
<item jid='romeo@example.net'/>
</query>
</iq>
If there are no contacts in the roster, then the server MUST return
an IQ-result containing a child <query/> element that in turn
contains no <item/> children (e.g., the server MUST NOT return an
empty <iq/> stanza element).
S: <iq to='juliet@example.com/chamber'
id='roster_result'
type='result'>
<query xmlns='jabber:iq:roster' ver='ver9'/>
</iq>
2.1.7. Subscription Attribute
The state of the presence subscription in relation to a roster item
is captured in the 'subscription' attribute of the <item/> element.
Allowable subscription-related values for this attribute are:
o "none" -- the user does not have a subscription to the contact's
presence, and the contact does not have a subscription to the
user's presence; this is the default value, so if the subscription
attribute is not included then the state is to be understood as
"none"
o "to" -- the user has a subscription to the contact's presence, but
the contact does not have a subscription to the user's presence
o "from" -- the contact has a subscription to the user's presence,
but the user does not have a subscription to the contact's
presence
o "both" -- both the user and the contact have subscriptions to each
other's presence (also called a "mutual subscription")
In a roster result, the client MUST ignore values of the
'subscription' attribute other than "none", "to", "from", or "both".
In a roster push, the client MUST ignore values of the 'subscription'
attribute other than "none", "to", "from", "both", or "remove".
Saint-Andre Expires October 2, 2010 [Page 14]

Internet-Draft XMPP IM March 2010
In a roster set, the value of the 'subscription' attribute MAY be
included with a value of "remove", which indicates that the item is
to be removed from the roster; the server MUST ignore all values of
the 'subscription' attribute other than "remove".
2.2. Retrieving the Roster on Login
Upon authenticating with a server and binding a resource (thus
becoming a connected resource), a client SHOULD request the roster
before sending initial presence (however, because receiving the
roster is not necessarily desirable for all resources, e.g., a
connection with limited bandwidth, the client's request for the
roster is not mandatory). After a connected resource sends initial
presence (see Section 4.2), it is referred to as an available
resource. If a connected resource or available resource requests the
roster, it is referred to as an INTERESTED RESOURCE. The server MUST
send roster pushes to all interested resources.
Note: Presence subscription requests are sent to available
resources, whereas the roster pushes associated with subscription
state changes are sent to interested resources. Therefore if a
resource wishes to receive both subscription requests and roster
pushes, it MUST both send initial presence and request the roster.
A client requests the roster by sending a roster get over its stream
to the server.
C: <iq from='juliet@example.com/balcony'
id='roster_1'
type='get'>
<query xmlns='jabber:iq:roster'/>
</iq>
Saint-Andre Expires October 2, 2010 [Page 15]

Internet-Draft XMPP IM March 2010
S: <iq id='roster_1'
to='juliet@example.com/balcony'
type='result'>
<query xmlns='jabber:iq:roster' ver='ver11'>
<item jid='romeo@example.net'
name='Romeo'
subscription='both'>
<group>Friends</group>
</item>
<item jid='mercutio@example.com'
name='Mercutio'
subscription='from'/>
<item jid='benvolio@example.net'
name='Benvolio'
subscription='both'/>
</query>
</iq>
If the server cannot process the roster get, it MUST return an
appropriate stanza error as described in [XMPP-CORE] (such as
<service-unavailable/> if the roster namespace is not supported or
<internal-server-error/> if the server experiences trouble processing
or returning the roster).
2.3. Adding a Roster Item2.3.1. Request
At any time, a client can add an item to the roster. This is done by
sending a roster set containing a new item.
C: <iq from='juliet@example.com/balcony'
id='roster_2'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='Nurse'>
<group>Servants</group>
</item>
</query>
</iq>
Note: When a user adds a contact for the purpose of tracking the
user's presence subscription to a contact, the user's client
SHOULD send a presence subscription request to the contact before
generating any roster set related to the contact. This enables
the user's server to enforce any policies relevant to presence
subscriptions (e.g., a prohibition on presence subscriptions to
Saint-Andre Expires October 2, 2010 [Page 16]

Internet-Draft XMPP IM March 2010
full JIDs). For details, see Section 3.
2.3.2. Success Case
If the server can successfully process the roster set (i.e., if none
of the error cases occurs), it MUST create the roster item in
persistent storage.
The server MUST then return an IQ stanza of type "result" to the
connected resource that sent the roster set.
S: <iq id='roster_2'
to='juliet@example.com/balcony'
type='result'/>
The server MUST also send a roster push containing the new roster
item to all of the user's interested resources, including the
resource that generated the roster set.
S: <iq to='juliet@example.com/balcony'
id='a78b4q6ha463'
type='set'>
<query xmlns='jabber:iq:roster' ver='ver13'>
<item jid='nurse@example.com'
name='Nurse'
subscription='none'>
<group>Servants</group>
</item>
</query>
</iq>
S: <iq to='juliet@example.com/chamber'
id='a78b4q6ha464'
type='set'>
<query xmlns='jabber:iq:roster' ver='ver13'>
<item jid='nurse@example.com'
name='Nurse'
subscription='none'>
<group>Servants</group>
</item>
</query>
</iq>
As mandated by the semantics of the IQ stanza as defined in
[XMPP-CORE], each resource that receives a roster push MUST reply
with an IQ stanza of type "result" (or "error").
Saint-Andre Expires October 2, 2010 [Page 17]

Internet-Draft XMPP IM March 2010
C: <iq from='juliet@example.com/balcony'
id='a78b4q6ha463'
type='result'/>
C: <iq from='juliet@example.com/chamber'
id='a78b4q6ha464'
type='result'/>
2.3.3. Error Cases
If the server cannot successfully process the roster set, it MUST
return a stanza error. The following error cases are defined
(naturally, other stanza errors can occur, such as <internal-server-
error/>).
The server SHOULD return a <bad-request/> stanza error to the client
if the roster set violates any of the following conditions:
1. The <query/> element contains more than one <item/> child
element.
2. The <item/> element contains more than one <group/> element, but
there are duplicate groups (where duplicates are determined using
the Resourceprep profile of stringprep as defined in
[XMPP-CORE]).
The server SHOULD return a <not-acceptable/> stanza error to the
client if the roster set violates any of the following conditions:
1. The value of the 'name' attribute is greater than a server-
configured limit.
2. The XML character data of the <group/> element is of zero length.
3. The XML character data of the <group/> element is greater than a
server-configured limit.
Alternatively, the server MAY ignore the foregoing violations and
process the roster set as best as possible (e.g., process only the
first <item/> element, ignore duplicate <group/> elements, place the
roster item in no group or a default group if the <group/> element is
empty, and truncate 'name' attributes and <group/> elements that are
too long).
Saint-Andre Expires October 2, 2010 [Page 18]

Internet-Draft XMPP IM March 20102.4. Updating a Roster Item2.4.1. Request
Updating an existing roster item is done in the same way as adding a
new roster item, i.e., by sending a roster set to the server.
Because a roster item is atomic, the item MUST be updated exactly as
provided in the roster set.
There are several reasons why a client might update a roster item:
1. Adding a group
2. Deleting a group
3. Changing the handle
4. Deleting the handle
Consider a roster item that is defined as follows:
<item jid='romeo@example.net'
name='Romeo'>
<group>Friends</group>
</item>
The user who has this item in her roster might want to add the item
to another group.
C: <iq from='juliet@example.com/balcony'
id='update_1'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
name='Romeo'>
<group>Friends</group>
<group>Lovers</group>
</item>
</query>
</iq>
The user might then want to remove the item from the original group.
Saint-Andre Expires October 2, 2010 [Page 22]

Internet-Draft XMPP IM March 20102.4.2. Success Case
As with adding a roster item, if the roster item can be successfully
processed then the server MUST update the roster information in
persistent storage, send a roster push to all of the user's
interested resources, and send an IQ result to the initiating
resource; for details, see Section 2.3.
2.4.3. Error Cases
The error cases described under Section 2.3.3 also apply to updating
a roster item.
2.5. Deleting a Roster Item2.5.1. Request
At any time, a client can delete an item from his or her roster by
sending a roster set and specifying the value of the 'subscription'
attribute to be "remove".
C: <iq from='juliet@example.com/balcony'
id='delete_1'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com' subscription='remove'/>
</query>
</iq>
2.5.2. Success Case
As with adding a roster item, if the server can successfully process
the roster set then it MUST update the roster information in
persistent storage, send a roster push to all of the user's
interested resources (with the 'subscription' attribute set to a
value of "remove"), and send an IQ result to the initiating resource;
for details, see Section 2.3.
If the user has a presence subscription to the contact or the contact
has a presence subscription to the user, the user's server MUST also
generate a presence stanza of type "unsubscribe" (to unsubscribe from
the contact's presence) or a presence stanza of type "unsubscribed"
(to cancel the contact's subscription to the user), or both.
Saint-Andre Expires October 2, 2010 [Page 24]

Internet-Draft XMPP IM March 20102.6.2. Request
If a client supports roster versioning and the server to which it has
connected advertises support for roster versioning as described in
the foregoing section, then the client MUST include the 'ver' element
in its request for the roster. If the server does not advertise
support for roster versioning, the client MUST NOT include the 'ver'
attribute. If the client includes the 'ver' attribute in its roster
get, it sets the attribute's value to the version ID associated with
its last cache of the roster.
C: <iq from='romeo@montague.lit/home'
id='r1h3vzp7'
to='romeo@montague.lit'
type='get'>
<query xmlns='jabber:iq:roster' ver='ver14'/>
</iq>
If the client has not yet cached the roster or the cache is lost or
corrupted, but the client wishes to bootstrap the use of roster
versioning, it MUST set the 'ver' attribute to the empty string
(i.e., ver="").
Naturally, if the client does not support roster versioning or does
not wish to bootstrap the use of roster versioning, it will not
include the 'ver' attribute.
2.6.3. Success Case
Whether or not the roster has been modified since the version ID
enumerated by the client, the server MUST either return the complete
roster as described under Section 2.1.6 (including a 'ver' attribute
that signals the latest version) or return an empty IQ-result (thus
indicating that any roster modifications will be sent via roster
pushes, as described below). In general, unless returning the
complete roster would (1) use less bandwidth than sending individual
roster pushes to the client (e.g., if the roster contains only a few
items) or (2) the server cannot associate the version ID with any
previous version it has on file, the server SHOULD send an empty IQ-
result and then send the modifications (if any) via roster pushes.
S: <iq from='romeo@montague.lit'
id='r1h3vzp7'
to='romeo@montague.lit/home'
type='result'/>
Note: This empty IQ-result is different from an empty <query/>
element, thus disambiguating this usage from an empty roster.
Saint-Andre Expires October 2, 2010 [Page 26]

Internet-Draft XMPP IM March 2010
If the roster has not been modified since the version ID enumerated
by the client, the server will simply not send any roster pushes to
the client (until and unless some relevant event triggers a roster
push during the lifetime of the client's session).
If the roster has been modified since the version ID enumerated by
the client, the server MUST then send one roster push to the client
for each roster item that has been modified since the version ID
enumerated by the client. (We call a roster push that is sent for
purposes of roster version synchronization an "interim roster push".)
Definition: A ROSTER MODIFICATION is any modification to the
roster data that would result in a roster push to a connected
client. Therefore internal states related to roster processing
within the server that would not result in a roster push to a
connected client do not necessitate a change to the version.
Saint-Andre Expires October 2, 2010 [Page 27]

Internet-Draft XMPP IM March 2010
1. Imagine that the client had an active presence session for the
entire time between its cached roster version (say, "ver14") and
the new roster version (say, "ver96").
2. During that time, the client might have received roster pushes
related to various roster versions. However, some of those
roster pushes might have contained intermediate updates to the
same roster item (e.g., modifications to the subscription state
for bill@shakespeare.lit from "none" to "to" and from "to" to
"both").
3. The interim roster pushes would not include all of the
intermediate steps, only the final result of all modifications
applied to each item while the client was in fact offline (say,
"ver34", "ver42", "ver72", and "ver96").
The client MUST handle an "interim roster push" in the same way it
handles any roster push (indeed, from the client's perspective it
cannot tell the difference between an "interim" roster push and a
"live" roster push). If the client's session ends before it receives
all of the interim roster pushes, when requesting the roster after
reconnection it SHOULD request the version associated with the last
roster push it received during the session that was disconnected, not
the version associated with the roster result it received at the
start of the session that was disconnected.
When roster versioning is enabled, the server MUST include the
updated roster version with each roster push. Roster pushes MUST
occur in order of modification and the version contained in a roster
push MUST be unique. Even if the client has not included the 'ver'
attribute in its roster gets or sets, the server SHOULD include the
'ver' attribute on all roster pushes and results that it sends to the
client.
Note: Implementation guidelines and more detailed examples for
roster versioning are provided in [XEP-0237].
3. Managing Presence Subscriptions
In order to protect the privacy of instant messaging users, presence
information is disclosed only to other entities that a user has
approved. When a user has agreed that another entity is allowed to
view its presence, the entity is said to have a SUBSCRIPTION to the
user's presence. An entity that has a subscription to a user's
presence or to which a user has a presence subscription is called a
CONTACT (in this document the term "contact" is also used in a less
strict sense to refer to a potential contact or an item in a user's
roster).
Saint-Andre Expires October 2, 2010 [Page 29]

Internet-Draft XMPP IM March 2010
In XMPP, a subscription lasts across presence sessions; indeed, it
lasts until the contact unsubscribes or the user cancels the
previously-granted subscription.
Subscriptions are managed within XMPP by sending presence stanzas
containing specially-defined attributes ("subscribe", "unsubscribe",
"subscribed", and "unsubscribed").
Note: When a server processes or generates an outbound presence
stanza of type "subscribe", "subscribed", "unsubscribe", or
"unsubscribed", the server MUST stamp the outgoing presence stanza
with the bare JID <node@domain> of the sending entity, not the
full JID <node@domain/resource>. Enforcement of this rule
simplifies the presence subscription model and helps to prevent
presence leaks; for information about presence leaks, refer to the
security considerations of [XMPP-CORE].
Subscription states are reflected in the rosters of both the user and
the contact. Complete details regarding these subscription states
can be found Appendix A; those details are not provided in this
section, which simply narrates the protocol flows for common use
cases related to presence subscriptions.
3.1. Requesting a Subscription
A SUBSCRIPTION REQUEST is a request from a user for authorization to
permanently subscribe to a contact's presence information;
syntactically it is a presence stanza whose 'type' attribute has a
value of "subscribe". A subscription request is generated by a
user's client, processed by the (potential) contact's server, and
acted on by the contact via the contact's client. The workflow is
described in the following sections.
Note: Presence subscription requests are sent to available
resources, whereas the roster pushes associated with subscription
state changes are sent to interested resources. Therefore if a
resource wishes to receive both subscription requests and roster
pushes, it MUST both send initial presence and request the roster.
3.1.1. Client Generation of Outbound Subscription Request
A user's client generates a subscription request by sending a
presence stanza of type "subscribe" and specifying a 'to' address of
the potential contact's bare JID <contact@domain>.
UC: <presence id='xk3h1v69'
to='juliet@example.com'
type='subscribe'/>
Saint-Andre Expires October 2, 2010 [Page 30]

Internet-Draft XMPP IM March 2010
When a user sends a presence subscription request to a potential
instant messaging and presence contact, the value of the 'to'
attribute MUST be a bare JID <contact@domain> rather a full JID
<contact@domain/resource>, since the desired result is for the user
to receive presence from all of the contact's resources, not merely
the particular resource specified in the 'to' attribute. Use of bare
JIDs also simplifies subscription processing, presence probes, and
presence notifications by the user's server and the contact's server.
For tracking purposes, a client SHOULD include an 'id' attribute in a
presence subscription request.
Note: Many XMPP clients prompt the user for information about the
potential contact (e.g., "handle" and desired roster group) when
generating an outbound presence subscription request and therefore
send a roster set before sending the outbound presence
subscription request. This behavior is OPTIONAL, because a client
MAY instead wait until receiving the initial roster push from the
server before uploading user-provided information about the
contact. A server MUST process a roster set and outbound presence
subscription request in either order.
3.1.2. Server Processing of Outbound Subscription Request
Upon receiving the outbound presence subscription request, the user's
server MUST proceed as follows.
1. Before processing the request, the user's server SHOULD check the
syntax of the JID contained in the 'to' attribute. If the JID is
of the form <contact@domain/resource> instead of
<contact@domain>, the user's server SHOULD treat it as if the
request had been directed to the contact's bare JID and modify
the 'to' address accordingly. The server MAY also verify that
the JID adheres to the format defined in [XMPP-CORE], including
checking against the relevant stringprep profiles.
2. If the potential contact is hosted on the same server as the
user, then the server MUST adhere to the rules specified in the
next section in processing the subscription request and
delivering it to the (local) contact.
3. If the potential contact is hosted on a remote server, subject to
local service policies the user's server MUST then route the
stanza to that remote domain in accordance with core XMPP stanza
processing rules. (This can result in returning an appropriate
stanza error to the user, such as <remote-server-timeout/>.)
As mentioned, before locally delivering or remotely routing the
presence subscription request, the user's server MUST stamp the
outbound subscription request with the bare JID <user@domain> of the
Saint-Andre Expires October 2, 2010 [Page 31]

Internet-Draft XMPP IM March 2010
user.
US: <presence from='romeo@example.net'
id='xk3h1v69'
to='juliet@example.com'
type='subscribe'/>
If the presence subscription request cannot be locally delivered or
remotely routed (e.g., because the request is malformed, the local
contact does not exist, the remote server does not exist, an attempt
to contact the remote server times out, or any other error determined
or experienced by the user's server), then the user's server MUST
return an appropriate error stanza to the user. An example follows.
US: <presence from='juliet@example.com'
id='xk3h1v69'
to='romeo@example.net'
type='error'>
<error type='modify'>
<remote-server-not-found
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</presence>
After locally delivering or remotely routing the presence
subscription request, the user's server MUST then send a roster push
to all of the user's interested resources, containing the potential
contact with a subscription state of "none" and with notation that
the subscription is pending (via an 'ask' attribute whose value is
"subscribe").
Saint-Andre Expires October 2, 2010 [Page 32]

Internet-Draft XMPP IM March 2010
US: <iq id='b89c5r7ib574'
to='romeo@example.net/foo'
type='set'>
<query xmlns='jabber:iq:roster'>
<item ask='subscribe'
jid='juliet@example.com'
subscription='none'/>
</query>
</iq>
US: <iq id='b89c5r7ib575'
to='romeo@example.net/bar'
type='set'>
<query xmlns='jabber:iq:roster'>
<item ask='subscribe'
jid='juliet@example.com'
subscription='none'/>
</item>
</query>
</iq>
If the contact does not approve or deny the subscription request
within some configurable amount of time, the user's server SHOULD
resend the subscription request to the contact based on an
implementation-specific algorithm (e.g., whenever a new resource
becomes available for the user, or after a certain amount of time has
elapsed); this helps to recover from transient, silent errors that
might have occurred in relation to the original subscription request.
3.1.3. Server Processing of Inbound Subscription Request
Before processing the inbound presence subscription request, the
contact's server SHOULD check the syntax of the JID contained in the
'to' attribute. If the JID is of the form <contact@domain/resource>
instead of <contact@domain>, the contact's server SHOULD treat it as
if the request had been directed to the contact's bare JID and modify
the 'to' address accordingly. The server MAY also verify that the
JID adheres to the format defined in [XMPP-CORE], including checking
against the relevant stringprep profiles.
When processing the inbound presence subscription request, the
contact's server MUST adhere to the following rules:
1. Above all, the contact's server MUST NOT automatically approve
subscription requests on the contact's behalf (unless the contact
has configured its account to automatically approve subscription
requests or has accepted an agreement with its service provider
that allows such behavior, for instance via an employment
Saint-Andre Expires October 2, 2010 [Page 33]

Internet-Draft XMPP IM March 2010
agreement within an enterprise deployment). Instead, if a
subscription request requires approval then the contact's server
MUST deliver that request to the contact's available resource(s)
for approval or denial by the contact.
2. If the contact does not exist, then the contact's server MUST
automatically return a presence stanza of type "unsubscribed" to
the user.
CS: <presence from='juliet@example.com'
id='xk3h1v69'
to='romeo@example.net'
type='unsubscribed'/>
3. If the contact exists and the user already has a subscription to
the contact's presence, then the contact's server MUST auto-reply
on behalf of the contact by sending a presence stanza of type
"subscribed" from the contact's bare JID to the user's bare JID.
If the contact previously sent a presence stanza of type
"subscribed" and the contact's server treated that as indicating
"pre-approval" for the user's presence subscription (see
Appendix A), then the contact's server SHOULD also auto-reply on
behalf of the contact.
CS: <presence from='juliet@example.com'
id='xk3h1v69'
to='romeo@example.net'
type='subscribed'/>
4. If the contact exists, the user does not already have a
subscription to the contact's presence, and there is at least one
available resource associated with the contact when the
subscription request is received by the contact's server, then
the contact's server MUST broadcast that subscription request to
all available resources in accordance with Section 8. As a way
of acknowledging receipt of the presence subscription request,
the contact's server MAY send a presence stanza of type
"unavailable" from the bare JID of the contact to the bare JID of
the user (the user's client MUST NOT assume that this ack
provides presence information about the contact, since it comes
from the contact's bare JID and is received before the
subscription request has been approved).
5. If the contact exists, the user does not already have a
subscription to the contact's presence, and the contact has no
available resources when the subscription request is received by
the contact's server, then the contact's server MUST keep a
record of the complete presence stanza comprising the
subscription request, including any extended content contained
therein, and deliver the request when the contact next has an
Saint-Andre Expires October 2, 2010 [Page 34]

Internet-Draft XMPP IM March 2010
available resource. The contact's server MUST continue to
deliver the subscription request whenever the contact creates an
available resource, until the contact either approves or denies
the request. (The contact's server MUST NOT deliver more than
one subscription request from any given user when the contact
next has an available resource; e.g., if the user sends multiple
subscription requests to the contact while the contact is
offline, the contact's server SHOULD store only one of those
requests, such as the first request or last request, and MUST
deliver only one of the requests when the contact next has an
available resource; this helps to prevent "subscription request
spam".) As a way of acknowledging receipt of the presence
subscription request, the contact's server MAY send a presence
stanza of type "unavailable" from the bare JID of the contact to
the bare JID of the user, since it comes from the contact's bare
JID and is received before the subscription request has been
approved).
Note: Until and unless the contact approves the subscription
request as described under Section 3.1.4, the contact's server
MUST NOT add an item for the user to the contact's roster.
3.1.4. Client Processing of Inbound Subscription Request
When the contact's client receives a subscription request from the
user, it MUST present the request to the contact for approval (unless
the contact has explicitly configured the client to automatically
approve or deny some or all subscription requests).
A subscription request is approved by sending a presence stanza of
type "subscribed", which is processed as described in the following
sections for both the contact's server and the user's server.
CC: <presence to='romeo@example.net' type='subscribed'/>
A subscription request is denied by sending a presence stanza of type
"unsubscribed", which is processed as described under Section 3.2 for
both the contact's server and the user's server.
CC: <presence to='romeo@example.net' type='unsubscribed'/>
3.1.5. Server Processing of Outbound Subscription Approval
When the contact's client sends the subscription approval, the
contact's server MUST stamp the outbound stanza with the bare JID
<contact@domain> of the contact and locally deliver or remotely route
the stanza to the user.
Saint-Andre Expires October 2, 2010 [Page 35]

Internet-Draft XMPP IM March 2010
CS: <presence from='juliet@example.com'
to='romeo@example.net'
type='subscribed'/>
The contact's server then MUST send a roster push to all of the
contact's interested resources.
CS: <iq id='a78b4q6ha463'
to='juliet@example.com/balcony'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='from'/>
</query>
</iq>
CS: <iq id='a78b4q6ha464'
to='juliet@example.com/chamber'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='from'/>
</query>
</iq>
The contact's server MUST then also send current presence to the user
from each of the contact's available resources.
CS: <presence from='juliet@example.com/balcony'
to='romeo@example.net'/>
CS: <presence from='juliet@example.com/chamber'
to='romeo@example.net'/>
From the perspective of the contact, there now exists a subscription
from the user.
In order to subscribe to the user's presence, the contact would then
send a subscription request to the user. (XMPP clients will often
automatically send the subscription request instead of requiring the
contact to initiate the subscription request, since it is assumed
that the desired end state is a mutual subscription.) Naturally,
when the contact sends a subscription request to the user, the
subscription states will be different from those shown in the
foregoing examples (see Appendix A) and the roles will be reversed.
Saint-Andre Expires October 2, 2010 [Page 36]

Internet-Draft XMPP IM March 20103.1.6. Server Processing of Inbound Subscription Approval
When the user's server receives the subscription approval, it MUST
first check if the contact is in the user's roster with
subscription='none' or subscription='from' and the 'ask' flag set to
"subscribe" (i.e., a subscription state of "None + Pending Out",
"None + Pending Out+In", or "From + Pending Out"; see Appendix A).
If this check is successful, the user's server MUST:
1. Deliver the inbound subscription approval to all of the user's
interested resources (this helps to give the user's client(s)
proper context regarding the subscription approval so that they
can differentiate between a roster push originated by another of
the user's resources and a subscription approval received from
the contact). This MUST occur before sending the roster push
described in the next step.
US: <presence from='juliet@example.com'
to='romeo@example.net'
type='subscribed'/>
2. Initiate a roster push to all of the user's interested resources,
containing an updated roster item for the contact with the
'subscription' attribute set to a value of "to" (if the
subscription state was "None + Pending Out" or "None + Pending
Out+In") or "both" (if the subscription state was "From + Pending
Out").
US: <iq id='b89c5r7ib576'
to='romeo@example.net/foo'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='to'/>
</query>
</iq>
US: <iq id='b89c5r7ib577'
to='romeo@example.net/bar'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='to'/>
</item>
</query>
</iq>
Saint-Andre Expires October 2, 2010 [Page 37]

Internet-Draft XMPP IM March 2010
3. The user's server MUST also deliver the available presence stanza
received from each of the contact's available resources to each
of the user's available resources.
[ ... to resource1 ... ]
US: <presence from='juliet@example.com/balcony'
to='romeo@example.net'/>
[ ... to resource2 ... ]
US: <presence from='juliet@example.com/balcony'
to='romeo@example.net'/>
[ ... to resource1 ... ]
US: <presence from='juliet@example.com/chamber'
to='romeo@example.net'/>
[ ... to resource2 ... ]
US: <presence from='juliet@example.com/chamber'
to='romeo@example.net'/>
Otherwise -- that is, if the user does not exist, if the contact is
not in the user's roster, or if the contact is in the user's roster
with a subscription state other than those described in the foregoing
check -- then the user's server MUST silently ignore the stanza by
not delivering it to the user, not modifying the user's roster, and
not generating a roster push to the user's interested resources.
From the perspective of the user, there now exists a subscription to
the contact's presence.
3.2. Cancelling a Subscription3.2.1. Client Generation of Subscription Cancellation
If a contact would like to cancel a subscription that it has
previously granted to a user (or deny a subscription request), it
sends a presence stanza of type "unsubscribed".
CC: <presence to='romeo@example.net' type='unsubscribed'/>
Saint-Andre Expires October 2, 2010 [Page 38]

Internet-Draft XMPP IM March 20103.2.2. Server Processing of Outbound Subscription Cancellation
Upon receiving the outound subscription cancellation, the contact's
server MUST proceed as follows.
1. If the user is hosted on the same server as the contact, then the
server MUST adhere to the rules specified in the next section in
processing the subscription cancellation.
2. If the user is hosted on a remote server, subject to local
service policies the contact's server MUST then route the stanza
to that remote domain in accordance with core XMPP stanza
processing rules. (This can result in returning an appropriate
stanza error to the contact, such as <remote-server-timeout/>.)
As mentioned, before locally delivering or remotely routing the
stanza, the contact's server MUST stamp the outbound subscription
cancellation with the bare JID <contact@domain> of the contact.
CS: <presence from='juliet@example.com'
to='romeo@example.net'
type='unsubscribed'/>
The contact's server then MUST send a roster push with the updated
roster item to all of the contact's interested resources, where the
subscription state is now either "none" or "to" (see Appendix A).
CS: <iq id='a78b4q6ha465'
to='juliet@example.com/balcony'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='none'/>
</query>
</iq>
CS: <iq id='a78b4q6ha466'
to='juliet@example.com/chamber'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='none'/>
</query>
</iq>
Saint-Andre Expires October 2, 2010 [Page 39]

Internet-Draft XMPP IM March 20103.2.3. Server Processing of Inbound Subscription Cancellation
When the user's server receives the inbound subscription
cancellation, it MUST first check if the contact is in the user's
roster with subscription='to' or subscription='both' (see
Appendix A). If this check is successful, the user's server MUST:
1. Deliver the inbound subscription cancellation to all of the
user's interested resources (this helps to give the user's
client(s) proper context regarding the subscription cancellation
so that they can differentiate between a roster push originated
by another of the user's resources and a subscription
cancellation received from the contact). This MUST occur before
sending the roster push described in the next step.
US: <presence from='juliet@example.com'
to='romeo@example.net'
type='unsubscribed'/>
2. Initiate a roster push to all of the user's interested resources,
containing an updated roster item for the contact with the
'subscription' attribute set to a value of "none" (if the
subscription state was "To" or "To + Pending In") or "from" (if
the subscription state was "Both").
US: <iq id='h37h3u1bv400'
to='romeo@example.net/foo'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='none'/>
</query>
</iq>
US: <iq id='h37h3u1bv401'
to='romeo@example.net/bar'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='none'/>
</item>
</query>
</iq>
Otherwise -- that is, if the user does not exist, if the contact is
not in the user's roster, or if the contact is in the user's roster
with a subscription state other than those described in the foregoing
check -- then the user's server MUST silently ignore the stanza by
Saint-Andre Expires October 2, 2010 [Page 40]

Internet-Draft XMPP IM March 2010
not delivering it to the user, not modifying the user's roster, and
not generating a roster push to the user's interested resources.
3.3. Unsubscribing3.3.1. Client Generation of Unsubscribe
If a user would like to unsubscribe from a contact's presence, it
sends a presence stanza of type "unsubscribe".
UC: <presence to='juliet@example.com' type='unsubscribe'/>
3.3.2. Server Processing of Outbound Unsubscribe
Upon receiving the outbound unsubscribe, the user's server MUST
proceed as follows.
1. If the contact is hosted on the same server as the user, then the
server MUST adhere to the rules specified in the next section in
processing the subscription request.
2. If the contact is hosted on a remote server, subject to local
service policies the user's server MUST then route the stanza to
that remote domain in accordance with core XMPP stanza processing
rules. (This can result in returning an appropriate stanza error
to the user, such as <remote-server-timeout/>.)
As mentioned, before locally delivering or remotely routing the
unsubscrbe, the user's server MUST stamp the stanza with the bare JID
<user@domain> of the user.
US: <presence from='romeo@example.net'
to='juliet@example.com'
type='unsubscribe'/>
The user's server then MUST send a roster push with the updated
roster item to all of the user's interested resources, where the
subscription state is now either "none" or "from" (see Appendix A).
Saint-Andre Expires October 2, 2010 [Page 41]

Internet-Draft XMPP IM March 2010
US: <iq id='h37h3u1bv402'
to='romeo@example.net/foo'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='none'/>
</query>
</iq>
US: <iq to='romeo@example.net/bar'
type='set'
id='h37h3u1bv403'>
<query xmlns='jabber:iq:roster'>
<item jid='juliet@example.com'
subscription='none'/>
</item>
</query>
</iq>
3.3.3. Server Processing of Inbound Unsubscribe
When the contact's server receives the unsubscribe notification, it
MUST first check if the user is in the contact's roster with
subscription='from' or subscription='both' (i.e., a subscription
state of "From", "From + Pending Out", or "Both"; see Appendix A).
If this check is successful, the contact's server MUST:
1. Deliver the inbound unsubscribe to all of the contact's
interested resources (this helps to give the contact's client(s)
proper context regarding the unsubscribe so that they can
differentiate between a roster push originated by another of the
contact's resources and an unsubscribe received from the user).
This MUST occur before sending the roster push described in the
next step.
CS: <presence from='romeo@example.net'
to='juliet@example.com'
type='unsubscribe'/>
2. Initiate a roster push to all of the contact's interested
resources, containing an updated roster item for the contact with
the 'subscription' attribute set to a value of "none" (if the
subscription state was "From" or "From + Pending Out") or "to"
(if the subscription state was "Both").
Saint-Andre Expires October 2, 2010 [Page 42]

Internet-Draft XMPP IM March 2010
CS: <iq id='a78b4q6ha467'
to='juliet@example.com/balcony'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='none'/>
</query>
</iq>
CS: <iq id='a78b4q6ha468'
to='juliet@example.com/chamber'
type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
subscription='none'/>
</query>
</iq>
3. Deliver the inbound unavailable notification to all of the
contact's interested resources.
CS: <presence from='romeo@example.net'
to='juliet@example.com'
type='unavailable'/>
Note: The user's client MUST NOT depend on receiving the unsubscribe
and the unavailable presence notification, since it MUST consider its
presence subscription to the contact, and its presence information
about the contact, to be null and void when it sends the presence
stanza of type "unusbscribe" or when receives the roster push
triggered by the unsubscribe request.
Otherwise -- that is, if the contact does not exist, if the user is
not in the contact's roster, or if the user is in the contact's
roster with a subscription state other than those described in the
foregoing check -- then the contact's server MUST silently ignore the
stanza by not delivering it to the contact, not modifying the
contact's roster, and not generating a roster push to the contact's
interested resources. However, if the contact's server is keeping
track of an inbound presence subscription request from the user to
the contact but the user is not in the contact's roster (functionally
equivalent to a subscription state of "None + Pending In" where the
contact never added the user to the contact's roster), then the
contact's server MUST simply remove any record of the inbound
presence subscription request (it cannot remove the user from the
contact's roster because the user was never added to the contact's
roster).
Saint-Andre Expires October 2, 2010 [Page 43]

Internet-Draft XMPP IM March 20104. Exchanging Presence Information4.1. Overview
The concept of presence refers to an entity's availability for
communication over a network. At the most basic level, presence is a
boolean "on/off" variable that signals whether an entity is available
or unavailable for communication (the terms "online" and "offline"
are also used). In XMPP, a user's availability is signalled when a
client controlled by the user generates a <presence/> stanza with no
'type' attribute, and an entity's lack of availability is signalled
when a client generates a <presence/> stanza whose 'type' attribute
has a value of "unavailable".
XMPP presence typically follows a "publish-subscribe" or "observer"
pattern, wherein an entity sends presence to its server, and its
server then broadcasts that information to all of the entity's
contacts who have a subscription to the entity's presence (in the
terminology of [IMP-MODEL], an entity that generates presence is a
"presentity" and the entities that receive presence are
"subscribers"). A client generates presence for broadcasting to all
subscribed entities by sending a presence stanza to its server with
no 'to' address, where the presence stanza has either no 'type'
attribute or a 'type' attribute whose value is "unavailable". This
kind of presence is called BROADCAST PRESENCE. (A client can also
send DIRECTED PRESENCE, i.e., a presence stanza with a 'to' address;
this is less common but is sometimes used to send presence to
entities that are not subscribed to the user's presence; see
Section 4.6.)
After a client completes the preconditions specified in [XMPP-CORE],
it can establish a PRESENCE SESSION at its server by sending initial
presence (Section 4.2), where the presence session is terminated by
sending unavailable presence (Section 4.5). For the duration of its
presence session, a connected resource (in the terminology of
[XMPP-CORE]) is said to be an AVAILABLE RESOURCE.
In XMPP-based applications that combine messaging and presence
functionality, the default type of communication for which presence
signals availability is messaging; however, it is not necessary for
XMPP-based applications to combine messaging and presence
functionality, and can provide standalone presence features without
messaging (in addition, XMPP servers do not require information about
network availability in order to successfully route message and IQ
stanzas).
Saint-Andre Expires October 2, 2010 [Page 44]

Internet-Draft XMPP IM March 2010
Note: In the following examples, the "user" is juliet@example.com
and the user has three contacts in her roster with a subscription
state of "from" or "both": romeo@example.net,
mercutio@example.com, and benvolio@example.net.
4.2. Initial Presence4.2.1. Client Generation of Initial Presence
After completing the preconditions described in [XMPP-CORE]
(REQUIRED) and requesting the roster (RECOMMENDED), a client signals
its availability for communication by sending INITIAL PRESENCE to its
server, i.e., a presence stanza with no 'to' address (indicating that
it is meant to be broadcast by the server on behalf of the client)
and no 'type' attribute (indicating the user's availability).
UC: <presence/>
The initial presence stanza MAY contain the <priority/> element, the
<show/> element, and one or more instances of the <status/> element,
as well as extended content.
4.2.2. Server Processing of Outbound Presence
Upon receiving initial presence from a client, the user's server MUST
send the initial presence stanza from the full JID
<user@domain/resource> of the user to all contacts that are
subscribed to the user's presence; such contacts are those for which
a JID is present in the user's roster with the 'subscription'
attribute set to a value of "from" or "both".
US: <presence from='juliet@example.com/balcony'
to='romeo@example.net'/>
US: <presence from='juliet@example.com/balcony'
to='mercutio@example.com'/>
US: <presence from='juliet@example.com/balcony'
to='benvolio@example.net'/>
The user's server MUST also broadcast initial presence from the
user's newly available resource to all of the user's available
resources (including the resource that generated the presence
notification in the first place).
Saint-Andre Expires October 2, 2010 [Page 45]

Internet-Draft XMPP IM March 2010
US: <presence from='juliet@example.com/balcony'
to='juliet@example.com/balcony'/>
US: <presence from='juliet@example.com/balcony'
to='juliet@example.com/chamber'/>
In the absence of presence information about the user's contacts, the
user's server MUST also send presence probes to the user's contacts
on behalf of the user as specified under Section 4.3.
4.2.3. Server Processing of Inbound Presence
Upon receiving presence from the user, the contact's server MUST
deliver the user's presence stanza to all of the contact's available
resources.
[ ... to resource1 ... ]
CS: <presence from='juliet@example.com/balcony'
to='romeo@example.net'/>
[ ... to resource2 ... ]
CS: <presence from='juliet@example.com/balcony'
to='romeo@example.net'/>
If there is no such contact, the contact's server MUST silently
ignore the presence stanza.
4.2.4. Client Processing of Inbound Presence
When the contact's client receives presence from the user, it SHOULD
proceed as follows:
1. If the user is in the contact's roster, the client MUST display
the presence information in an appropriate roster interface.
2. If the user is not in the contact's roster but the contact and
the user are actively exchanging message or IQ stanzas, the
contact's client SHOULD display the presence information in the
user interface for that chat session (see also Section 4.6 and
Section 5.1).
3. Otherwise, the client MUST ignore the presence information and
not display it to the contact.
4.3. Presence Probes
A PRESENCE PROBE is a request for a contact's current presence
information, sent on behalf of a user by the user's server;
Saint-Andre Expires October 2, 2010 [Page 46]

Internet-Draft XMPP IM March 2010
syntactically it is a presence stanza whose 'type' attribute has a
value of "probe". In the context of presence subscriptions, the
value of the 'from' address MUST be the bare or full JID of the
subscribed user and the value of the 'to' address SHOULD be the bare
JID of the contact to which the user is subscribed (since presence
subscriptions are based on the bare JID) but MAY be a full JID for
the contact. (Probes can also be sent outside the context of a
presence subscription, e.g. when the contact has sent directed
presence to an entity as described under Section 4.6.)
US: <presence from='juliet@example.com/balcony'
id='ign291v5'
to='romeo@example.net'
type='probe'/>
Note: Although presence probes MAY be sent by a client, in general
a client will not need to send them since the task of gathering
presence from a user's contacts is managed by the user's server.
However, if a client generates an outbound presence probe then the
user's server SHOULD route the probe (if the contact is at another
server) or process the probe (if the contact is at the same
server) and MUST NOT return a stanza or stream error to the
client.
4.3.1. Server Generation of Outbound Presence Probe
When a server needs to discover the availability of a user's contact,
it sends a presence probe from the full JID <user@domain/resource> of
the user to the bare JID <contact@domain> of the contact. The server
MUST NOT send a probe to a contact if the user is not subscribed to
the contact's presence (i.e., if the contact is not in the user's
roster with the 'subscription' attribute set to a value of "to" or
"both".
The user's server SHOULD send a presence probe whenever the user
starts a new presence session by sending initial presence; however,
the server MAY choose not to send the probe at that point if it has
what it deems to be reliable and up-to-date presence information
about the user's contacts (e.g., because the user has another
available resource or because the user briefly logged off and on
before the new presence session began). In addition, a server MAY
periodically send a presence probe to a contact if it has not
received presence information or other traffic from the contact in
some configurable amount of time; this can help to prevent "ghost"
contacts who appear to be online but in fact are not.
Saint-Andre Expires October 2, 2010 [Page 47]

Internet-Draft XMPP IM March 2010
US: <presence from='juliet@example.com/balcony'
id='ign291v5'
to='romeo@example.net'
type='probe'/>
US: <presence from='juliet@example.com/balcony'
id='xv291f38'
to='mercutio@example.com'
type='probe'/>
Naturally, the user's server does not need to send a presence probe
to a contact if the contact's account resides on the same server as
the user, since the server possesses contact's information locally.
4.3.2. Server Processing of Inbound Presence Probe
Upon receiving a presence probe to the contact's bare JID from the
user's server on behalf of the user, the contact's server SHOULD
reply as follows:
1. If the contact account does not exist or the user is in the
contact's roster with a subscription state other than "From",
"From + Pending Out", or "Both" (as defined under Appendix A) and
the contact has not sent directed presence to the user (as
defined under Section 4.6), then the contact's server MUST return
a presence stanza of type "unsubscribed" in response to the
presence probe (however, if a server receives a presence probe
from a configured hostname of the server itself or another such
trusted service, it MAY provide presence information about the
user to that entity).
CS: <presence from='mercutio@example.com'
id='xv291f38'
to='juliet@example.com'
type='unsubscribed'/>
2. Else, if the contact has moved temporarily or permanently to
another address, then the server SHOULD return a presence stanza
of type "error" with a stanza error condition of <redirect/>
(temporary) or <gone/> (permanent) that includes the new address
of the contact.
Saint-Andre Expires October 2, 2010 [Page 48]

Internet-Draft XMPP IM March 2010
CS: <presence from='mercutio@example.com'
id='xv291f38'
to='juliet@example.com'
type='error'>
<error type='modify'>
<gone xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>
xmpp:la-mer@example.com
</gone>
</error>
</presence>
3. Else, if the contact has no available resources, then the server
SHOULD reply to the presence probe by sending to the user a
presence stanza of type "unavailable" (although sending
unavailable presence here is preferable because it results in a
deterministic answer to the probe, it is not mandatory because it
can greatly increase the number of presence notifications
generated by the contact's server); if appropriate in accordance
with local security policies this presence notification MAY
include the full XML of the last unavailable presence stanza that
the server received from the contact (including the 'id' of the
original stanza), but if not then the presence notification
SHOULD simply indicate that the contact is unavailable without
any of the details originally provided; in any case the presence
notification returned to the probing entity SHOULD include
information about the time when the last unavailable presence
stanza was generated (formatted using the XMPP delayed delivery
extension [DELAY]).
CS: <presence from='mercutio@example.com'
id='xv291f38'
to='juliet@example.com'
type='unavailable'>
<delay xmlns='urn:xmpp:delay'
stamp='2002-09-10T23:41:07Z'/>
</presence>
4. Else, if the contact has at least one available resource, then
the server MUST reply to the presence probe by sending to the
user the full XML of the last presence stanza with no 'to'
attribute received by the server from each of the contact's
available resources.
Saint-Andre Expires October 2, 2010 [Page 49]

Internet-Draft XMPP IM March 2010
CS: <presence from='romeo@example.net/foo'
id='hzf1v27k'
to='juliet@example.com'/>
CS: <presence from='romeo@example.net/bar'
id='ps6t1fu3'
to='juliet@example.com'>
<show>away</show>
</presence>
If the contact's server receives a presence probe addressed to a full
JID of the contact, the server MUST NOT return presence information
about any resource except the resource specified by the 'to' address
of the probe. Rules #1 and #2 for a bare JID probe apply equally to
the case of a full JID probe. If there is a resource matching the
full JID and (a) the probing entity has authorization via a presence
subscription to see the contact's presence or (b) the contact has
sent directed available presence to the probing entity, then the
server MUST return an available presence notification, which SHOULD
communicate only the fact that the resource is available (not
detailed information such as the <show/>, <status/>, <priority/>, or
presence extensions).
CS: <presence from='romeo@example.net/bar'
to='lobby@chat.example.com'/>
Note: The handling of the 'id' attribute in relation to presence
probes was unspecified in the predecessor to this specification.
Although the pattern of "send a probe and receive a reply" might
seem like a request-response protocol, in fact it is not because
the response to a probe might consist of multiple presence stanzas
(one for each available resource currently active for the
contact). For this reason, if the contact currently has available
resources then the contact's server SHOULD preserve the 'id'
attribute of the contact's original presence stanza (if any) when
sending those presence notifications to the probing entity;
however, if the contact currently has no available resources, the
probing entity is not authorized (via presence subscription) to
see the contact's presence, or an error occurs in relation to the
proble, then the contact's server SHOULD mirror the 'id' of the
presence probe when replying to the probing entity.
4.4. Subsequent Presence BroadcastSaint-Andre Expires October 2, 2010 [Page 50]

Internet-Draft XMPP IM March 20104.4.1. Client Generation of Presence Broadcast
After sending initial presence, the user's client can update its
availability for broadcasting at any time during its session by
sending a presence stanza with no 'to' address and no 'type'
attribute.
UC: <presence>
<show>away</show>
</presence>
The presence broadcast MAY contain the <priority/> element, the
<show/> element, and one or more instances of the <status/> element,
as well as extended content.
However, a user SHOULD send a presence update only to broadcast
information that is relevant to the user's availability for
communication or the communication capabilities of the connected
resource. Information that is not relevant in this way can be of
interest to the user's contacts but SHOULD be sent via other means,
such as the XMPP message stanza.
4.4.2. Server Processing of Outbound Presence
Upon receiving a presence stanza expressing updated availability, the
user's server MUST broadcast the full XML of that presence stanza to
the contacts who meet all of the following criteria:
1. The contact is in the user's roster with a subscription type of
"from" or "both".
2. The last presence stanza received from the contact during the
user's presence session was not of type "error" or "unsubscribe".
As an optimization, if the subscription type is "both", then the
server SHOULD send subsequent presence notifications to a contact
only if the contact is online according to the user's server. That
is, if the user's server never received a positive indication that
the contact is online in response to the presence probe it sent to
the contact or if the last presence stanza it received from the
contact during the user's presence session was of type "unavailable",
the user's server SHOULD NOT send subsequent presence notifications
from the user to the contact. This optimization helps to save
bandwidth, since most presence subscriptions are bidirectional and
many contacts will not be online at any given time.
Saint-Andre Expires October 2, 2010 [Page 51]

Internet-Draft XMPP IM March 2010
US: <presence from='juliet@example.com/balcony'
to='romeo@example.net'>
<show>away</show>
</presence>
US: <presence from='juliet@example.com/balcony'
to='benvolio@example.net'>
<show>away</show>
</presence>
US: <presence from='juliet@example.com/balcony'
to='mercutio@example.com'>
<show>away</show>
</presence>
See Section 4.6 regarding rules that supplement the foregoing for
handling of directed presence.
The user's server MUST also send the presence stanza to all of the
user's available resources (including the resource that generated the
presence notification in the first place).
US: <presence from='juliet@example.com/balcony'
to='juliet@example.com/chamber'>
<show>away</show>
</presence>
US: <presence from='juliet@example.com/balcony'
to='juliet@example.com/balcony'>
<show>away</show>
</presence>
4.4.3. Server Processing of Inbound Presence
Upon receiving presence from the user, the contact's server MUST
deliver the user's presence stanza to all of the contact's available
resources.
Saint-Andre Expires October 2, 2010 [Page 52]

Internet-Draft XMPP IM March 2010
[ ... to resource1 ... ]
CS: <presence from='juliet@example.com/balcony'
to='romeo@example.net'>
<show>away</show>
</presence>
[ ... to resource2 ... ]
CS: <presence from='juliet@example.com/balcony'
to='romeo@example.net'>
<show>away</show>
</presence>
4.4.4. Client Processing of Inbound Presence
When the contact's client receives presence from the user, it SHOULD
proceed as follows:
1. If the user is in the contact's roster, the client MUST display
the presence information in an appropriate roster interface.
2. If the user is not in the contact's roster but the contact and
the user are actively exchanging message or IQ stanzas, the
contact's client SHOULD display the presence information in the
user interface for that chat session (see also Section 4.6 and
Section 5.1).
3. Otherwise, the client MUST ignore the presence information and
not display it to the contact.
4.5. Unavailable Presence4.5.1. Client Generation of Unavailable Presence
Before ending its presence session with a server, the user's client
SHOULD gracefully become unavailable by sending UNAVAILABLE PRESENCE,
i.e., a presence stanza that possesses no 'to' attribute and that
possesses a 'type' attribute whose value is "unavailable".
UC: <presence type='unavailable'/>
Optionally, the unavailable presence stanza MAY contain one or more
<status/> elements specifying the reason why the user is no longer
available.
UC: <presence type='unavailable'>
<status>going on vacation</status>
</presence>
Saint-Andre Expires October 2, 2010 [Page 53]

Internet-Draft XMPP IM March 2010
However, the unavailable presence stanza MUST NOT contain the
<priority/> element or the <show/> element, since these elements
apply only to available presence.
4.5.2. Server Processing of Outbound Unavailable Presence
The user's server MUST NOT depend on receiving unavailable presence
from an available resource, since the resource can become unavailable
ungracefully (e.g., the resource can be timed out by the server
because of inactivity).
If an available resource becomes unavailable for any reason (either
gracefully or ungracefully), the user's server MUST broadcast
unavailable presence to all contacts that meet all of the following
criteria:
1. The contact is in the user's roster with a subscription type of
"from" or "both".
2. The last presence stanza received from the contact during the
user's presence session was not of type "error" or "unsubscribe".
See Section 4.6 regarding rules that supplement the foregoing for
handling of directed presence.
The optimization employed for subsequent presence broadcast during
a user's presence session MUST NOT be employed for unavailable
presence broadcast; if it were, the last presence received by the
contact's server would be the user's initial presence for the
presence session, with the result that the contact would consider
the user to be online.
If the unavailable notification was gracefully received from the
client, then the server MUST broadcast the full XML of the presence
stanza.
Saint-Andre Expires October 2, 2010 [Page 54]

Internet-Draft XMPP IM March 2010
US: <presence from='juliet@example.com/balcony'
to='romeo@example.net'
type='unavailable'/>
<status>going on vacation</status>
</presence>
US: <presence from='juliet@example.com/balcony'
to='benvolio@example.net'
type='unavailable'>
<status>going on vacation</status>
</presence>
US: <presence from='juliet@example.com/balcony'
to='mercutio@example.com'
type='unavailable'>
<status>going on vacation</status>
</presence>
The user's server MUST also send the unavailable notification to all
of the user's available resources (including the resource that
generated the presence notification in the first place).
US: <presence from='juliet@example.com/balcony'
to='juliet@example.com/chamber'
type='unavailable'>
<status>going on vacation</status>
</presence>
If the server detects that the user has gone offline ungracefully,
then the server MUST generate the unavailable presence broadcast on
the user's behalf.
Note: Any presence stanza with no 'type' attribute and no 'to'
attribute that is sent after sending unavailable presence
broadcast MUST be sent by the user's server to all subscribers
(i.e., MUST be treated as equivalent to initial presence for a new
presence session).
4.5.3. Server Processing of Inbound Unavailable Presence
Upon receiving an unavailable notification from the user, the
contact's server MUST deliver the user's presence stanza to all of
the contact's available resources.
Saint-Andre Expires October 2, 2010 [Page 55]

Internet-Draft XMPP IM March 2010
[ ... to resource1 ... ]
CS: <presence from='juliet@example.com/balcony'
to='romeo@example.net'
type='unavailable'>
<status>going on vacation</status>
</presence>
[ ... to resource2 ... ]
CS: <presence from='juliet@example.com/balcony'
to='romeo@example.net'
type='unavailable'>
<status>going on vacation</status>
</presence>
If the contact's server is optimizing subsequent presence delivery as
described under Section 4.4, it MUST also note that the user is
unavailable and appropriately update its internal representation of
which entities are online.
4.5.4. Client Processing of Inbound Unavailable Presence
When the contact's client receives an unavailable notification from
the user, it SHOULD proceed as follows:
1. If the user is in the contact's roster, the client MUST display
the unavailable notification in an appropriate roster interface.
2. If the user is not in the contact's roster but the contact and
the user are actively exchanging message or IQ stanzas, the
contact's client SHOULD display the unavailable notification in
the user interface for that chat session (see also Section 4.6
and Section 5.1).
3. Otherwise, the client MUST ignore the unavailable notification
and not display it to the contact.
Typically, presence is presence about a particular connected
resource. However, it is possible for the contact to receive an
unavailable notification from the bare JID of the user. In this
case, the presence notificatio SHOULD be treated as related to a
resource identifier of zero length, which does not supersede or
overshadow other resources associated with the same bare JID.
4.6. Directed Presence
This section supplements and in some respects modifies the rules for
client and server processing of presence notifications, but only for
the special case of directed presence.
Saint-Andre Expires October 2, 2010 [Page 56]

Internet-Draft XMPP IM March 20104.6.1. Client Generation of Directed Presence
As noted, directed presence is a presence stanza with a 'to'
attribute whose value is the bare JID or full JID of the other entity
and with either no 'type' attribute (indicating availability) or a
'type' attribute whose value is "unavailable".
Information about the use of directed presence in the context of a
one-to-one chat session is provided under Section 5.1.
4.6.2. Server Processing of Outbound Directed Presence
When the user's server receives a directed presence stanza, it SHOULD
process it according to the following rules.
1. If the user sends directed available or unavailable presence to a
contact that is in the user's roster with a subscription type of
"from" or "both" after having sent initial presence and before
sending unavailable presence broadcast (i.e., during the user's
presence session), the user's server MUST locally deliver or
remotely route the full XML of that presence stanza but SHOULD
NOT otherwise modify the contact's status regarding presence
broadcast (i.e., it SHOULD include the contact's JID in any
subsequent presence broadcasts initiated by the user).
2. If the user sends directed presence to an entity that is not in
the user's roster with a subscription type of "from" or "both"
after having sent initial presence and before sending unavailable
presence broadcast (i.e., during the user's presence session),
the user's server MUST locally deliver or remotely route the full
XML of that presence stanza to the entity but MUST NOT modify the
contact's status regarding available presence broadcast (i.e., it
MUST NOT include the entity's JID in any subsequent broadcasts of
available presence initiated by the user); however, if the
available resource from which the user sent the directed presence
becomes unavailable, the user's server MUST route that
unavailable presence to the entity (if the user has not yet sent
directed unavailable presence to that entity).
3. If the user sends directed presence without first sending initial
presence or after having sent unavailable presence broadcast
(i.e., the resource is connected but not available), the user's
server MUST treat the entity to which the user sends directed
presence as in case #2 above.
4.6.3. Server Processing of Inbound Directed Presence
From the perspective of the contact's server, there is no difference
between presence broadcast and directed presence, so the contact's
server follows the existing rules for processing of inbound presence.
Saint-Andre Expires October 2, 2010 [Page 57]

Internet-Draft XMPP IM March 20104.6.4. Client Processing of Inbound Directed Presence
When the contact's client receives directed presence from the user,
it SHOULD proceed as follows:
1. If the user is in the contact's roster, the client MUST display
the presence information in an appropriate roster interface.
2. If the user is not in the contact's roster but the contact and
the user are actively exchanging message or IQ stanzas, the
contact's client SHOULD display the presence information in the
user interface for that chat session (see also Section 4.6 and
Section 5.1).
3. Otherwise, the client MUST ignore the presence information and
not display it to the contact.
4.7. Presence Syntax4.7.1. Type Attribute
The absence of a 'type' attribute signals that the relevant entity is
available for communication (see Section 4.2 and Section 4.4).
A 'type' attribute with a value of "unavailable" signals that the
relevant entity is not available for communication (see Section 4.5).
The XMPP presence stanza is also used to negotiate and manage
subscriptions to the presence of other entities. These tasks are
completed via presence stanzas of type "subscribe", "unsubscribe",
"subscribed", and "unsubscribed" as described under Section 3.
If a user and contact are associated with different XMPP servers,
those servers also use a special presence stanza of type "probe" in
order to determine the availability of the entity on the peer server;
for details, see Section 4.3. Clients SHOULD NOT send presence
stanzas of type "probe".
The values of the 'type' attribute can be summarized as follows:
o error -- An error has occurred regarding processing of a
previously-sent presence stanza; if the presence stanza is of type
"error", it MUST include an <error/> child element (refer to
[XMPP-CORE]).
o probe -- A request for an entity's current presence; SHOULD be
generated only by a server on behalf of a user.
o subscribe -- The sender wishes to subscribe to the recipient's
presence.
Saint-Andre Expires October 2, 2010 [Page 58]

Internet-Draft XMPP IM March 2010
o subscribed -- The sender has allowed the recipient to receive
their presence.
o unavailable -- Signals that the entity is no longer available for
communication.
o unsubscribe -- The sender is unsubscribing from the receiver's
presence.
o unsubscribed -- The subscription request has been denied or a
previously-granted subscription has been cancelled.
If the value of the 'type' attribute is not one of the foregoing
values, the recipient or an intermediate router SHOULD return a
stanza error of <bad-request/>.
Note: There is no default value for the 'type' attribute of the
<presence/> element; in particular, there is no value of
"available".
4.7.2. Child Elements
In accordance with the default namespace declaration, a presence
stanza is qualified by the 'jabber:client' or 'jabber:server'
namespace, which defines certain allowable children of presence
stanzas, in particular the <show/>, <status/>, and <priority/>
elements. These child elements are used to provide more detailed
information about an entity's availability. Typically these child
elements are provided only if the presence stanza possesses no 'type'
attribute, although exceptions are noted in the text that follows.
4.7.3. Show Element
The OPTIONAL <show/> element specifies the particular availability
sub-state of an entity or a specific resource thereof. A presence
stanza MUST NOT contain more than one <show/> element. There are no
attributes defined for the <show/> element. The XML character data
of the <show/> element is not human-readable. The XML character data
MUST be one of the following (additional availability states could be
defined through a child element of the presence stanza that is
qualified by a namespace other than the default namespace):
o away -- The entity or resource is temporarily away.
o chat -- The entity or resource is actively interested in chatting.
o dnd -- The entity or resource is busy (dnd = "Do Not Disturb").
o xa -- The entity or resource is away for an extended period (xa =
"eXtended Away").
If no <show/> element is provided, the entity is assumed to be online
and available.
Saint-Andre Expires October 2, 2010 [Page 59]

Internet-Draft XMPP IM March 2010
Any specialized processing of availability states by recipients and
intermediate routers is up to the implementation (e.g., incorporation
of availability states into stanza routing and delivery logic).
4.7.4. Status Element
The OPTIONAL <status/> element contains human-readable XML character
data specifying a natural-language description of an entity's
availability. It is normally used in conjunction with the show
element to provide a detailed description of an availability state
(e.g., "In a meeting") when the presence stanza has no 'type'
attribute.
<presence from='romeo@example.net/orchard'
xml:lang='en'>
<show>dnd</show>
<status>Wooing Juliet</status>
</presence>
There are no attributes defined for the <status/> element, with the
exception of the 'xml:lang' attribute inherited from XML. Multiple
instances of the <status/> element MAY be included, but only if each
instance possesses an 'xml:lang' attribute with a distinct language
value (either explicitly or by inheritance from the 'xml:lang' value
of an element farther up in the XML hierarchy, which can include the
XML stream header as described in [XMPP-CORE]).
<presence from='romeo@example.net/orchard'
xml:lang='en'>
<show>dnd</show>
<status>Wooing Juliet</status>
<status xml:lang='cs'>Dvo&#x0159;&#x00ED;m se Julii</status>
</presence>
A presence stanza of type "unavailable" MAY also include a <status/>
element to provide detailed information about why the entity is going
offline.
<presence from='romeo@example.net/orchard'
type='unavailable'
xml:lang='en'>
<status>Busy IRL</status>
</presence>
The <status/> child MAY also be sent in a subscription-related
presence stanza (i.e., type "subscribe", "subscribed", "unsubscribe",
or "unsubscribed") to provide a description of the action. The
receiving client MAY present this <status/> information to a human
Saint-Andre Expires October 2, 2010 [Page 60]

Internet-Draft XMPP IM March 2010
user (see Section 11).
<presence from='romeo@example.net'
to='nurse@example.com'
type='subscribe'>
<status>Hi, Juliet told to add you to my buddy list.</status>
</presence>
4.7.5. Priority Element
The OPTIONAL <priority/> element contains non-human-readable XML
character data that specifies the priority level of the resource.
The value MUST be an integer between -128 and +127. A presence
stanza MUST NOT contain more than one <priority/> element. There are
no attributes defined for the <priority/> element.
<presence xml:lang='en'>
<show>dnd</show>
<status>Wooing Juliet</status>
<status xml:lang='cs'>Dvo&#x0159;&#x00ED;m se Julii</status>
<priority>1</priority>
</presence>
If no priority is provided, the processing server or client MUST
consider the priority to be zero ("0").
The client's server MAY override the priority value provided by the
client (e.g., in order to impose a message handling rule of
delivering a message intended for the account's bare JID to all of
the account's available resources); if the server does so, it MUST
include the modified priority value (typically zero) when it echoes
the client's presence back to itself.
For information regarding the semantics of priority values in stanza
processing within instant messaging and presence applications, refer
to Section 8.
4.7.6. Extended Content
As described in [XMPP-CORE], an XML stanza MAY contain any child
element that is qualified by a namespace other than the default
namespace; this applies to the presence stanza as well.
(In the following example, the presence stanza includes entity
capabilities information as defined in [XEP-0115]).)
Saint-Andre Expires October 2, 2010 [Page 61]

Internet-Draft XMPP IM March 2010
<presence from='romeo@example.net'>
<c xmlns='http://jabber.org/protocol/caps'
hash='sha-1'
node='http://psi-im.org'
ver='q07IKJEyjvHSyhy//CH0CxmKi8w='/>
</presence>
Any extended content included in a presence stanza SHOULD represent
aspects of an entity's availability for communication or provide
information about communication-related capabilities.
5. Exchanging Messages
Once a client has authenticated with a server and bound a resource to
an XML stream as described in [XMPP-CORE], an XMPP server will route
XML stanzas to and from that client. One kind of stanza that can be
exchanged is <message/> (if, that is, messaging functionality is
enabled and the server is not a presence-only service). Exchanging
messages is a basic use of XMPP and occurs when a user generates a
message stanza that is addressed to another entity. As defined under
Section 8, the sender's server is responsible for delivering the
message to the intended recipient (if the recipient is on the same
local server) or for routing the message to the recipient's server
(if the recipient is on a remote server). Thus a message stanza is
used to "push" information to another entity.
5.1. One-to-One Chat Sessions
In practice, instant messaging activity between human users tends to
occur in form of a conversational burst that we call a CHAT SESSION:
the exchange of at least several messages between two parties in
relatively rapid succession within a relatively brief period of time.
When a human user intends to engage in such a chat session with a
contact (rather than sending a single message to which no reply is
expected), the user's client SHOULD send a message of type "chat" and
the contact's client SHOULD preserve that message type in subsequent
replies. The user's client also SHOULD include a <thread/> element
with its initial message, which the contact's client SHOULD also
preserve during the life of the chat session.
The user's client MUST address the initial message in a chat session
to the bare JID <contact@domain> of the contact (rather than
attempting to guess an appropriate full JID <contact@domain/resource>
based on the <show/>, <status/>, or <priority/> value of any presence
notifications it has received from the contact). Until and unless
the user's client receives a reply from the contact, it MUST continue
Saint-Andre Expires October 2, 2010 [Page 62]

Internet-Draft XMPP IM March 2010
sending any further messages to the contact's bare JID. The
contact's client SHOULD address its subsequent replies to the user's
full JID <user@domain/resource> as provided in the 'from' address of
the initial message. Once the user's client receives a reply from
the contact's full JID, it SHOULD address its subsequent messages to
the contact's full JID as provided in the 'from' address of the
contact's replies, thus "locking in" on that full JID.
When two parties engage in a chat session but do not share presence
with each other based on a presence subscription, they SHOULD send
directed presence to each other so that either party can easily
discover if the peer changes its availability or goes offline during
the course of the chat session. However, a client MUST provide a way
for a user to disable such presence sharing globally or to enable it
only with particular entities. Furthermore, a party SHOULD send
directed unavailable to the peer when it has reason to believe that
the chat session is over (e.g., if, after some reasonable amount of
time, no subsequent messages have been exchanged between the
parties).
If a party receives a presence change from the peer during a one-to-
one chat session (e.g., a new resource comes online or the existing
resource sends modified presence), then it SHOULD address its next
message(s) in the chat session to the bare JID of the peer (thus
"unlocking" the previous "lock") until it receives a message from one
of the peer's full JIDs.
An example of a chat session is provided under Section 7.
5.2. Message Syntax
The following sections describe the syntax of the <message/> stanza.
5.2.1. To Attribute
An instant messaging client specifies an intended recipient for a
message by providing the JID of an entity other than the sender in
the 'to' attribute of the <message/> stanza.
If the message is being sent outside the context of any existing chat
session or received message, the value of the 'to' address SHOULD be
of the form <user@domain> rather than of the form
<user@domain/resource>.
Saint-Andre Expires October 2, 2010 [Page 63]

Internet-Draft XMPP IM March 2010
<message
from='juliet@example.com/balcony'
to='romeo@example.net'
type='chat'
xml:lang='en'>
<body>Art thou not Romeo, and a Montague?</body>
</message>
If the message is being sent in reply to a message previously
received from an address of the form <user@domain/resource> (e.g.,
within the context of a one-to-one chat session as described under
Section 5.1), the value of the 'to' address SHOULD be of the form
<user@domain/resource> rather than of the form <user@domain> unless
the sender has knowledge (via presence) that the intended recipient's
resource is no longer available.
<message
from='romeo@example.net/orchard'
to='juliet@example.com/balcony'
type='chat'
xml:lang='en'>
<body>Neither, fair saint, if either thee dislike.</body>
</message>
5.2.2. Type Attribute
Common uses of the message stanza in instant messaging applications
include: single messages; messages sent in the context of a one-to-
one chat session; messages sent in the context of a multi-user chat
room; alerts, notifications, or other information to which no reply
is expected; and errors. These uses are differentiated via the
'type' attribute. Inclusion of the 'type' attribute is RECOMMENDED.
If included, the 'type' attribute MUST have one of the following
values:
o chat -- The message is sent in the context of a one-to-one chat
session. Typically a receiving client will present message of
type "chat" in an interface that enables one-to-one chat between
the two parties, including an appropriate conversation history.
Detailed recommendations regarding one-to-one chat sessions are
provided under Section 5.1.
o error -- The message is generated by an entity that experiences an
error in processing a message received from another entity (for
details regarding stanza error syntax, refer to [XMPP-CORE]). A
client that receives a message of type "error" SHOULD present an
appropriate interface informing the sender of the nature of the
error.
Saint-Andre Expires October 2, 2010 [Page 64]

Internet-Draft XMPP IM March 2010
o groupchat -- The message is sent in the context of a multi-user
chat environment (similar to that of [IRC]). Typically a
receiving client will present a message of type "groupchat" in an
interface that enables many-to-many chat between the parties,
including a roster of parties in the chatroom and an appropriate
conversation history. For detailed information about XMPP-based
groupchat, refer to [XEP-0045].
o headline -- The message provides an alert, a notification, or
other information to which no reply is expected (e.g., news
headlines, sports updates, near-real-time market data, and
syndicated content). Because no reply to the message is expected,
typically a receiving client will present a message of type
"headline" in an interface that appropriately differentiates the
message from standalone messages, chat messages, or groupchat
messages (e.g., by not providing the recipient with the ability to
reply). The receiving server SHOULD deliver the message to all of
the recipient's available resources.
o normal -- The message is a standalone message that is sent outside
the context of a one-to-one conversation or groupchat, and to
which it is expected that the recipient will reply. Typically a
receiving client will present a message of type "normal" in an
interface that enables the recipient to reply, but without a
conversation history. The default value of the 'type' attribute
is "normal".
An IM application SHOULD support all of the foregoing message types.
If an application receives a message with no 'type' attribute or the
application does not understand the value of the 'type' attribute
provided, it MUST consider the message to be of type "normal" (i.e.,
"normal" is the default).
Although the 'type' attribute is OPTIONAL, it is considered polite to
mirror the type in any replies to a message; furthermore, some
specialized applications (e.g., a multi-user chat service) MAY at
their discretion enforce the use of a particular message type (e.g.,
type='groupchat').
5.2.3. Body Element
The <body/> element contains human-readable XML character data that
specifies the textual contents of the message; this child element is
normally included but is OPTIONAL.
Saint-Andre Expires October 2, 2010 [Page 65]

Internet-Draft XMPP IM March 2010
<message
from='juliet@example.com/balcony'
to='romeo@example.net'
type='chat'
xml:lang='en'>
<body>Wherefore art thou, Romeo?</body>
</message>
There are no attributes defined for the <body/> element, with the
exception of the 'xml:lang' attribute. Multiple instances of the
<body/> element MAY be included in a message stanza, but only if each
instance possesses an 'xml:lang' attribute with a distinct language
value (either explicitly or by inheritance from the 'xml:lang' value
of an element farther up in the XML hierarchy, which can include the
XML stream header as described in [XMPP-CORE]).
<message
from='juliet@example.com/balcony'
to='romeo@example.net'
type='chat'
xml:lang='en'>
<body>Wherefore art thou, Romeo?</body>
<body xml:lang='cs'>
Pro&#x010D;e&#x017D; jsi ty, Romeo?
</body>
</message>
The <body/> element MUST NOT contain mixed content (as defined in
Section 3.2.2 of [XML]).
5.2.4. Subject Element
The <subject/> element contains human-readable XML character data
that specifies the topic of the message.
<message
from='juliet@example.com/balcony'
to='romeo@example.net'
type='chat'
xml:lang='en'>
<subject>I implore you!</subject>
<body>Wherefore art thou, Romeo?</body>
</message>
There are no attributes defined for the <subject/> element, with the
exception of the 'xml:lang' attribute inherited from XML. Multiple
instances of the <subject/> element MAY be included for the purpose
of providing alternate versions of the same subject, but only if each
Saint-Andre Expires October 2, 2010 [Page 66]

Internet-Draft XMPP IM March 2010
instance possesses an 'xml:lang' attribute with a distinct language
value (either explicitly or by inheritance from the 'xml:lang' value
of an element farther up in the XML hierarchy, which can include the
XML stream header as described in [XMPP-CORE]).
<message
from='juliet@example.com/balcony'
to='romeo@example.net'
type='chat'
xml:lang='en'>
<subject>I implore you!</subject>
<subject xml:lang='cs'>
&#x00DA;p&#x011B;nliv&#x011B; pros&#x00ED;m!
</subject>
<body>Wherefore art thou, Romeo?</body>
<body xml:lang='cs'>
Pro&#x010D;e&#x017E; jsi ty, Romeo?
</body>
</message>
The <subject/> element MUST NOT contain mixed content (as defined in
Section 3.2.2 of [XML]).
5.2.5. Thread Element
The primary use of the XMPP <thread/> element is to uniquely identify
a conversation thread or "chat session" between two entities
instantiated by <message/> stanzas of type 'chat'. However, the XMPP
<thread/> element can also be used to uniquely identify an analogous
thread between two entities instantiated by <message/> stanzas of
type 'headline' or 'normal', or among multiple entities in the
context of a multi-user chat room instantiated by <message/> stanzas
of type 'groupchat'. It MAY also be used for <message/> stanzas not
related to a human conversation, such as a game session or an
interaction between plugins. The <thread/> element is not used to
identify individual messages, only conversations or messagingg
sessions.
The inclusion of the <thread/> element is OPTIONAL. Because the
<thread/> element uniquely identifies the particular conversation
thread to which a message belongs, a message stanza MUST NOT contain
more than one <thread/> element.
The value of the <thread/> element is not human-readable and MUST be
treated as opaque by entities; no semantic meaning can be derived
from it, and only exact comparisons can be made against it. The
value of the <thread/> element MUST be a universally unique
identifier (UUID) as described in [UUID].
Saint-Andre Expires October 2, 2010 [Page 67]

Internet-Draft XMPP IM March 2010
The <thread/> element MAY possess a 'parent' attribute that
identifies another thread of which the current thread is an offshoot
or child; the value of the 'parent' MUST conform to the syntax of the
<thread/> element itself.
The <thread/> element MUST NOT contain mixed content (as defined in
Section 3.2.2 of [XML]).
<message
from='juliet@example.com/balcony'
to='romeo@example.net'
type='chat'
xml:lang='en'>
<subject>I implore you!</subject>
<subject xml:lang='cs'>
&#x00DA;p&#x011B;nliv&#x011B; pros&#x00ED;m!
</subject>
<body>Wherefore art thou, Romeo?</body>
<body xml:lang='cs'>
Pro&#x010D;e&#x017E; jsi ty, Romeo?
</body>
<thread parent='e0ffe42b28561960c6b12b944a092794b9683a38'>
0e3141cd80894871a68e6fe6b1ec56fa
</thread>
</message>
For detailed recommendations regarding use of the <thread/> element,
refer to [XEP-0201].
5.3. Extended Content
As described in [XMPP-CORE], an XML stanza MAY contain any child
element that is qualified by a namespace other than the default
namespace; this applies to the message stanza as well.
(In the following example, the message stanza includes an XHTML-
formatted version of the message as defined in [XEP-0071]).)
Saint-Andre Expires October 2, 2010 [Page 68]

Internet-Draft XMPP IM March 2010
<message
from='juliet@example.com/balcony'
to='romeo@example.net'
type='chat'
xml:lang='en'>
<body>Wherefore art thou, Romeo?</body>
<html xmlns='http://jabber.org/protocol/xhtml-im'>
<body xmlns='http://www.w3.org/1999/xhtml'>
Wherefore <span style='font-style: italic'>art</span>
thou, <span style='color:red'>Romeo</span>?
</body>
</html>
</message>
6. Exchanging IQ Stanzas
As described in [XMPP-CORE], IQ stanzas provide a structured request-
response mechanism. The basic semantics of that mechanism (e.g.,
that the 'id' attribute is mandatory) are defined in [XMPP-CORE],
whereas the specific semantics needed to complete particular use
cases are defined in all instances by the extended namespace that
qualifies the direct child element of an IQ stanza of type "get" or
"set". The 'jabber:client' and 'jabber:server' namespaces do not
define any children of IQ stanzas other than the <error/> element
common to all stanza types. This document defines one such extended
namespace, for Managing the Roster (Section 2). However, an IQ
stanza MAY contain structured information qualified by any extended
namespace.
As noted under Section 4.6, if a user exchanges IQ stanzas with
another entity but does not share presence with the entity based on a
presence subscription, it is RECOMMENDED for the user's client to
send directed presence to the other entity.
7. A Sample Session
The examples in this section illustrate a possible instant messaging
and presence session. The user is romeo@example.net, he has an
available resource whose resource identifier is "orchard", and he has
the following individuals in his roster:
o juliet@example.com (subscription="both" and she has two available
resources, one whose resource identifier is "chamber" and another
whose resource identifier is "balcony")
Saint-Andre Expires October 2, 2010 [Page 69]

Internet-Draft XMPP IM March 20108. Server Rules for Processing XML Stanzas
Basic server rules for processing XML stanzas are defined in
[XMPP-CORE]. This section defines supplementary rules for XMPP
instant messaging and presence servers; in the absence of a
supplementary rule defined below (e.g., for stanzas without a 'to'
address), the rule defined in [XMPP-CORE] applies.
8.1. No Such User
If the user account identified by the 'to' attribute does not exist,
how the stanza is processed depends on the stanza type.
o For an IQ stanza, the server MUST return a <service-unavailable/>
stanza error to the sender.
o For a message stanza, the server MUST return a <service-
unavailable/> stanza error to the sender.
o For a presence stanza with no 'type' attribute or a 'type'
attribute of "unavailable", the server MUST silently ignore the
stanza.
o For a presence stanza of type "subscribe", the server MUST return
a presence stanza of type "unsubscribed".
o For a presence stanza of type "subscribed", "unsubscribe", or
"unsubscribed", the server MUST silently ignore the stanza.
o For a presence stanza of type "probe", the server MUST return a
presence stanza of type "unsubscribed".
8.2. Full JID at Local Domain
If the hostname of the domain identifier portion of the JID contained
in the 'to' attribute of an inbound stanza matches one of the
configured hostnames of the server itself and the JID contained in
the 'to' attribute is of the form <user@domain/resource>, then the
server MUST adhere to the following rules (subject to enforcement of
relevant privacy and security policies, such as those deployed by
means of [XEP-0016] or [XEP-0191]).
8.2.1. Resource Matches
If an available or connected resource exactly matches the full JID,
how the stanza is processed depends on the stanza type.
o For an IQ stanzas of type "get" or "set", if the intended
recipient does not share presence with the requesting entity
either by means of a presence subscription of type "both" or
"from" or by means of directed presence, then the server SHOULD
NOT deliver the IQ stanza but instead SHOULD return a <service-
unavailable/> stanza error to the requesting entity. This policy
Saint-Andre Expires October 2, 2010 [Page 77]

Internet-Draft XMPP IM March 2010
helps to prevent presence leaks (see Section 11).
o For a message stanza, the server MUST deliver the stanza to the
resource.
o For a presence stanza with no 'type' attribute or a 'type'
attribute of "unavailable", the server MUST deliver the stanza to
the resource.
o For a presence stanza of type "subscribe", the server MUST follow
the guidelines provided under Section 3.1.3.
o For a presence stanza of type "subscribe", "subscribed",
"unsubscribe", or "unsubscribed", the server MUST follow the
guidelines provided under Section 3.
o For a presence stanza of type "probe", the server MUST follow the
guidelines provided under Section 4.3.
8.2.2. No Resource Matches
If no connected or available resource exactly matches the full JID,
how the stanza is processed depends on the stanza type.
o For an IQ stanza, the server MUST return a <service-unavailable/>
stanza error to the sender.
o For a message stanza of type "chat", "headline", or "normal", the
server SHOULD treat the stanza as if it were addressed to
<user@domain> as described in the next section (but without
modifying the value of the 'to' attribute).
o For a message stanza of type "error", the server MUST silently
ignore the stanza.
o For a message stanza of type "groupchat", the server MUST return a
stanza error to the sender, which SHOULD be <service-
unavailable/>.
o For a presence stanza with no 'type' attribute or a 'type'
attribute of "unavailable", the server MUST silently ignore the
stanza.
o For a presence stanza of type "subscribe", the server MUST follow
the guidelines provided under Section 3.1.3.
o For a presence stanza of type "subscribed", "unsubscribe", or
"unsubscribed", the server MUST ignore the stanza.
o For a presence stanza of type "probe", the server MUST follow the
guidelines provided under Section 4.3.
8.3. Bare JID at Local Domain
If the hostname of the domain identifier portion of the JID contained
in the 'to' attribute of an inbound stanza matches one of the
configured hostnames of the server itself and the JID contained in
the 'to' attribute is of the form <user@domain>, then the server MUST
adhere to the following rules.
Saint-Andre Expires October 2, 2010 [Page 78]

Internet-Draft XMPP IM March 20108.3.1. Available or Connected Resources
If there is at least one available or connected resource, how the
stanza is processed depends on the stanza type.
8.3.1.1. Message
For a message stanza of type "headline", the server MUST deliver the
stanza to all available resources.
For a message stanza of type "chat" or "normal", the server MUST
either (a) deliver the stanza to the highest-priority available
resource(s), or (b) deliver the stanza to all available resources
with non-negative presence priority. In the case of (a), if there is
not one highest-priority available resource but instead the highest
priority is asserted by two or more available resources, these
resources are said to form a "delivery tie". If there is a delivery
tie, a server SHOULD deliver the message to all of the tied
resources. However, before delivering the message, a server MAY
remove one or more resources from the tie. Methods for doing so are
outside the scope of this specification, but could include factors
such as the resource's time of connection, time of last network or
application activity, availability as determined by some hierarchy of
<show/> values, or user-configured rules. Nevertheless, a server
MUST NOT remove all resources from the tie, and MUST deliver the
message to at least one of the highest-priority resources (subject to
appropriate security policies as described under Section 11 and in
[XMPP-CORE]).
For a message stanza of type "groupchat", the server MUST NOT deliver
the stanza to any of the available resources but instead MUST return
a stanza error to the sender, which SHOULD be <service-unavailable/>.
For a message stanza of type "error", the server MUST silently
discard the message (i.e., neither deliver it to the intended
recipient nor return a stanza error to the sender).
However, for any message type the server MUST NOT deliver the stanza
to any available resource with a negative priority; if the only
available resource has a negative priority, the server SHOULD handle
the message as if there were no available or connected resources as
described under Section 8.3.2.
In all cases, the server MUST NOT rewrite the 'to' attribute (i.e.,
it MUST leave it as <user@domain> rather than change it to
<user@domain/resource>).
Saint-Andre Expires October 2, 2010 [Page 79]

Internet-Draft XMPP IM March 20108.3.1.2. Presence
For a presence stanza with no type or of type "unavailable", the
server MUST deliver it to all available resources.
For a presence stanza of type "subscribe", "subscribed",
"unsubscribe", or "unsubscribed", the server MUST adhere to the rules
defined under Section 3 and summarized under Appendix A.
For a presence stanza of type "probe", the server MUST handle it
directly as described under Section 4.3.
In all cases, the server MUST NOT rewrite the 'to' attribute (i.e.,
it MUST leave it as <user@domain> rather than change it to
<user@domain/resource>).
8.3.1.3. IQ
For an IQ stanza, the server itself MUST reply on behalf of the user
with either an IQ result or an IQ error, and MUST NOT deliver the IQ
stanza to any of the user's available resources. Specifically, if
the semantics of the qualifying namespace define a reply that the
server can provide on behalf of the user, then the server MUST reply
to the stanza on behalf of the user by returning either an IQ stanza
of type "result" or an IQ stanza of type "error" that is appropriate
to the original payload; if not, then the server MUST reply with a
<service-unavailable/> stanza error.
8.3.2. No Available or Connected Resources
If there are no available or connected resources associated with the
user, how the stanza is processed depends on the stanza type.
8.3.2.1. Message
In order to properly handle message stanzas, it is RECOMMENDED for an
implementation to support OFFLINE STORAGE, i.e., the server SHOULD
store the message stanza on behalf of the user and deliver it when
the user next becomes available. For recommendations regarding
offline message storage refer to [XEP-0160].
For a message stanza of type "chat" or "normal", the server SHOULD
add the message to offline storage or forward the message to the user
via a non-XMPP messaging system (e.g., to the user's email account).
However, if offline message storage or message forwarding is not
enabled or available (e.g., because a size limit has been reached on
offline messages), then the server MUST return a <service-
unavailable/> stanza error to the sender.
Saint-Andre Expires October 2, 2010 [Page 80]

Internet-Draft XMPP IM March 2010
For a message stanza of type "headline", according to local service
policies the server MUST either (a) add the message to offline
storage or (b) silently discard the message (i.e., neither deliver it
to the intended recipient nor return an error to the sender).
For a message stanza of type "groupchat", the server SHOULD NOT add
the message to offline storage but instead SHOULD return an error to
the sender.
For a message stanza of type "error", the server MUST NOT add the
message to offline storage but instead MUST silently discard the
message (i.e., neither deliver it to the intended recipient nor
return an error to the sender).
8.3.2.2. Presence
For a presence stanza with no type or of type "unavailable", the
server SHOULD silently ignore the stanza by not storing it for later
delivery and not replying to it on behalf of the user.
For a presence stanza of type "subscribe", "subscribed",
"unsubscribe", or "unsubscribed", the server MUST adhere to the rules
defined under Section 3 and summarized under Appendix A.
For a presence stanza of type "probe", the server MUST handle it
directly as described under Section 4.3.
8.3.2.3. IQ
For an IQ stanza, the server itself MUST reply on behalf of the user
with either an IQ result or an IQ error. Specifically, if the
semantics of the qualifying namespace define a reply that the server
can provide on behalf of the user, then the server MUST reply to the
stanza on behalf of the user by returning either an IQ stanza of type
"result" or an IQ stanza of type "error" that is appropriate to the
original payload; if not, then the server MUST reply with a <service-
unavailable/> stanza error.
8.4. Remote Domain
If the hostname of the domain identifier portion of the address
contained in the 'to' attribute of an outbound stanza does not match
a configured hostname of the server itself, then the server MUST
attempt to route the stanza to the remote domain. If there exists an
active stream between the two peers, then the server MUST route the
stanza over that stream for processing by the peer server. If not,
then the server MUST do the following.
Saint-Andre Expires October 2, 2010 [Page 81]

Internet-Draft XMPP IM March 2010
First, resolve the hostname of the remote domain (or use a cached
resolution of the remote domain to an IP address). The RECOMMENDED
order of attempted resolutions is as follows:
1. Attempt to resolve the remote hostname using a DNS service
location record [SRV] Service of "xmpp-server" and a Proto of
"tcp", resulting in resource records such as "_xmpp-
server._tcp.example.com.", as specified in [XMPP-CORE].
2. If the "xmpp-server" address record resolution fails, attempt to
resolve the "_im" or "_pres" SRV Service as specified in
[IMP-SRV], using the "_im" Service for <message/> stanzas and the
"_pres" Service for <presence/> stanzas (it is up to the
implementation how to handle <iq/> stanzas). This will result in
one or more resolutions of the form "_im.<proto>.example.com." or
"_pres.<proto>.example.com.", where "<proto>" would be a label
registered in the Instant Messaging SRV Protocol Label registry
or the Presence SRV Protocol Label registry: either "_xmpp" for
an XMPP-aware domain or some other IANA-registered label (e.g.,
"_simple") for a non-XMPP-aware domain.
3. If both SRV address record resolutions fail, attempt to perform a
normal IPv4/IPv6 address record resolution to determine the IP
address using the "xmpp-server" port of 5269 registered with the
IANA, as specified in [XMPP-CORE].
If the server cannot resolve the remote domain, it MUST return a
<remote-server-not-found/> stanza error.
Second, negotiate XML streams with the remote domain by following the
process defined in [XMPP-CORE]. If the server can resolve the remote
domain but cannot establish streams with the XMPP service at that
domain, it MUST return a <remote-server-timeout/> stanza error.
Third, route the stanza to the remote domain for processing by the
peer server.
Note: Administrators of server deployments are strongly encouraged
to keep the _im._xmpp, _pres._xmpp, and _xmpp._tcp SRV records
properly synchronized, since different implementations might
perform the "_im" and "_pres" lookups before the "xmpp-server"
lookup.
9. Handling of URIs
The addresses of XMPP entities as used in communication over an XMPP
network (e.g., in the 'from' and 'to' addresses of an XML stanza)
MUST NOT be prepended with a Uniform Resource Identifier [URI]
scheme. However, an application that is external to XMPP itself
Saint-Andre Expires October 2, 2010 [Page 82]

Internet-Draft XMPP IM March 2010
(e.g., a page on the World Wide Web) might need to identify an XMPP
entity either as a URI or as an Internationalized Resource Identifier
[IRI], and an XMPP client might need to interact with such an
external application (for example, an XMPP client might be invoked by
clicking a link provided on a web page).
In the context of such interactions, an XMPP client SHOULD handle
addresses that are encoded as "xmpp:" URIs and IRIs as specified in
[XMPP-URI] and further described in [XEP-0147]. A client SHOULD also
handle addresses that are encoded as "im:" URIs as specified in
[CPIM] and "pres:" URIs as specified in [CPP], although it MAY do so
by removing the "im:" or "pres:" scheme and entrusting address
resolution to the server as specified under Section 8.4.
10. Internationalization Considerations
For internationalization considerations, refer to the relevant
section of [XMPP-CORE].
11. Security Considerations
Core security considerations for XMPP are defined in the relevant
section of [XMPP-CORE].
Additional considerations that apply only to instant messaging and
presence applications of XMPP are defined in several places within
this document; specifically:
o When a server processes an inbound presence stanza of type "probe"
whose intended recipient is a user associated with one of the
server's hostnames, the server MUST NOT reveal the user's presence
if the sender is an entity that is not authorized to receive that
information as determined by presence subscriptions (see
Section 4).
o A user's server MUST NOT leak the user's network availability to
entities who are not authorized to know the user's presence,
either via an explicit subscription as described herein or via an
existing trust relationship (such as presence-enabled user
directories within organizations).
o When a server processes an outbound presence stanza with no type
or of type "unavailable", it MUST follow the rules defined under
Section 4 in order to ensure that such presence information is not
sent to entities that are not authorized to know such information.
o A client MAY ignore the <status/> element when contained in a
presence stanza of type "subscribe", "unsubscribe", "subscribed",
or "unsubscribed"; this can help prevent "presence subscription
Saint-Andre Expires October 2, 2010 [Page 83]

Internet-Draft XMPP IM March 2010
spam".
12. IANA Considerations
The following sections update the registrations provided in
[RFC3921].
For a number of related IANA considerations, refer to the relevant
section of [XMPP-CORE].
12.1. Instant Messaging SRV Protocol Label Registration
Address Resolution for Instant Messaging and Presence [IMP-SRV]
defines an Instant Messaging SRV Protocol Label registry for
protocols that can provide services that conform to the "_im" SRV
Service label. Because XMPP is one such protocol, the IANA registers
the "_xmpp" protocol label in the appropriate registry, as follows:
Protocol label: _xmpp
Specification: XXXX
Description: Instant messaging protocol label for the Extensible
Messaging and Presence Protocol (XMPP) as defined by XXXX.
Registrant Contact: IETF, XMPP Working Group, <xmppwg@xmpp.org>
12.2. Presence SRV Protocol Label Registration
Address Resolution for Instant Messaging and Presence [IMP-SRV]
defines a Presence SRV Protocol Label registry for protocols that can
provide services that conform to the "_pres" SRV Service label.
Because XMPP is one such protocol, the IANA registers the "_xmpp"
protocol label in the appropriate registry, as follows:
Protocol label: _xmpp
Specification: XXXX
Description: Presence protocol label for the Extensible Messaging
and Presence Protocol (XMPP) as defined by XXXX.
Registrant Contact: IETF, XMPP Working Group, <xmppwg@xmpp.org>
13. Conformance Requirements
This section describes a protocol feature set that summarizes the
conformance requirements of this specification. This feature set is
appropriate for use in software certification, interoperability
testing, and implementation reports. For each feature, this section
provides the following information:
Saint-Andre Expires October 2, 2010 [Page 84]

Internet-Draft XMPP IM March 2010
o A human-readable name
o An informational description
o A reference to the particular section of this document that
normatively defines the feature
o Whether the feature applies to the Client role, the Server role,
or both (where "N/A" signifies that the feature is not applicable
to the specified role)
o Whether the feature MUST or SHOULD be implemented, where the
capitalized terms are to be understood as described in [TERMS]
Note: The feature set specified here attempts to adhere to the
concepts and formats proposed by Larry Masinter within the IETF's
NEWTRK Working Group in 2005, as captured in [INTEROP]. Although
this feature set is more detailed than called for by [REPORTS], it
provides a suitable basis for the generation of implementation
reports to be submitted in support of advancing this specification
from Proposed Standard to Draft Standard in accordance with
[PROCESS].
Feature: message-body
Description: Support the <body/> child element of the <message/>
stanza.
Section: Section 5.2.3
Roles: Client MUST, Server N/A.
Feature: message-subject
Description: Support the <subject/> child element of the <message/>
stanza.
Section: Section 5.2.4
Roles: Client SHOULD, Server N/A.
Feature: message-thread
Description: Support the <thread/> child element of the <message/>
stanza.
Section: Section 5.2.5
Roles: Client SHOULD, Server N/A.
Feature: message-type
Description: Differentiate between messages of type "normal",
"chat", "groupchat", "headline", and "error".
Section: Section 5.2.2
Roles: Client MUST, Server N/A.
Feature: presence-notype
Saint-Andre Expires October 2, 2010 [Page 85]

Internet-Draft XMPP IM March 2010
Description: Treat a presence stanza with no 'type' attribute as
indicating availability.
Section: Section 4.7.1
Roles: Client MUST, Server MUST.
Feature: presence-probe
Description: Send and receive presence stanzas with a 'type'
attribute of "probe" for the discovery of presence information.
Section: Section 4.7.1
Roles: Client N/A, Server MUST.
Feature: presence-sub-approval
Description: Treat an outbound presence stanza of type "subscribed"
as the act of approving a presence subscription request previously
received from another entity, and treat an inbound presence stanza
of type "subscribed" as a subscription approval from another
entity.
Section: Section 3.1
Roles: Client MUST, Server MUST.
Feature: presence-sub-cancel
Description: Treat an outbound presence stanza of type
"unsubscribed" as the act of denying a subscription request
received from another entity or cancelling a subscription approval
previously granted to another entity, and treat an inbound
presence stanza of type "unsubscribed" as an subscription denial
or cancellation from another entity.
Section: Section 3.2
Roles: Client MUST, Server MUST.
Feature: presence-sub-request
Description: Treat an outbound presence stanza of type "subscribe"
as the act of requesting a subscription to the presence
information of another entity, and treat an inbound presence
stanza of type "subscribe" as a presence subscription request from
another entity.
Section: Section 3.1
Roles: Client MUST, Server MUST.
Feature: presence-sub-unsubscribe
Description: Treat an outbound presence stanza of type "unsubscribe"
as the act of unsubscribing from another entity, and treat an
inbound presence stanza of type "unsubscribe" as an unsubscribe
notification from another entity.
Saint-Andre Expires October 2, 2010 [Page 86]

Internet-Draft XMPP IM March 2010A.1. Defined States
There are four primary subscription states (note: these states are
described from the perspective of the user, not the contact):
o None -- the user does not have a subscription to the contact's
presence, and the contact does not have a subscription to the
user's presence
o To -- the user has a subscription to the contact's presence, but
the contact does not have a subscription to the user's presence
o From -- the contact has a subscription to the user's presence, but
the user does not have a subscription to the contact's presence
o Both -- both the user and the contact have subscriptions to each
other's presence (i.e., the union of 'from' and 'to')
These states are supplemented by various pending sub-states to yield
nine possible subscription states:
1. "None" = contact and user are not subscribed to each other, and
neither has requested a subscription from the other; this is
reflected in the user's roster by subscription='none'
2. "None + Pending Out" = contact and user are not subscribed to
each other, and user has sent contact a subscription request but
contact has not replied yet; this is reflected in the user's
roster by subscription='none' and ask='subscribe'
3. "None + Pending In" = contact and user are not subscribed to each
other, and contact has sent user a subscription request but user
has not replied yet; this state might or might not be reflected
in the user's roster, as follows: if the user has created a
roster item for the contact then the server MUST maintain that
roster item and also note the existence of the inbound presence
subscription request, whereas if the user has not created a
roster item for the contact then the user's server MUST note the
existence of the inbound presence subscription request but MUST
NOT create a roster item for the contact (instead, the server
MUST wait until the user has approved the subscription request
before adding the contact to the user's roster).
4. "None + Pending Out+In" = contact and user are not subscribed to
each other, contact has sent user a subscription request but user
has not replied yet, and user has sent contact a subscription
request but contact has not replied yet; this is reflected in the
user's roster by subscription='none' and ask='subscribe'
5. "To" = user is subscribed to contact (one-way); this is reflected
in the user's roster by subscription='to'
6. "To + Pending In" = user is subscribed to contact, and contact
has sent user a subscription request but user has not replied
yet; this is reflected in the user's roster by subscription='to'
Saint-Andre Expires October 2, 2010 [Page 91]

Internet-Draft XMPP IM March 2010
7. "From" = contact is subscribed to user (one-way); this is
reflected in the user's roster by subscription='from'
8. "From + Pending Out" = contact is subscribed to user, and user
has sent contact a subscription request but contact has not
replied yet; this is reflected in the user's roster by
subscription='from' and ask='subscribe'
9. "Both" = user and contact are subscribed to each other (two-way);
this is reflected in the user's roster by subscription='both'
A.2. Server Processing of Outbound Presence Subscription Stanzas
Outbound presence subscription stanzas enable the user to manage his
or her subscription to the contact's presence (via the "subscribe"
and "unsubscribe" types), and to manage the contact's access to the
user's presence (via the "subscribed" and "unsubscribed" types).
The following rules apply to outbound routing of the stanza as well
as changes to the user's roster.
Note: The rules for server processing of outbound presence
subscription stanzas are described from the perspective of the
user, not the contact. In addition, "S.N." stands for SHOULD NOT.
A.2.1. Subscribe
Table 1: Processing of outbound "subscribe" stanzas
+-----------------------------------------------------------------+
| EXISTING STATE | ROUTE? | NEW STATE |
+-----------------------------------------------------------------+
| "None" | MUST | "None + Pending Out" |
| "None + Pending Out" | MUST | no state change |
| "None + Pending In" | MUST | "None + Pending Out+In" |
| "None + Pending Out+In" | MUST | no state change |
| "To" | MUST | no state change |
| "To + Pending In" | MUST | no state change |
| "From" | MUST | "From + Pending Out" |
| "From + Pending Out" | MUST | no state change |
| "Both" | MUST | no state change |
+-----------------------------------------------------------------+
Note: A state change to "pending out" includes setting the 'ask'
flag to a value of "subscribe" in the user's roster.
Saint-Andre Expires October 2, 2010 [Page 92]

Internet-Draft XMPP IM March 2010A.3.1. Subscribe
Table 5: Processing of inbound "subscribe" stanzas
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
| "None" | MUST [1] | "None + Pending In" |
| "None + Pending Out" | MUST | "None + Pending Out+In" |
| "None + Pending In" | S.N. | no state change |
| "None + Pending Out+In" | S.N. | no state change |
| "To" | MUST | "To + Pending In" |
| "To + Pending In" | S.N. | no state change |
| "From" | S.N. [2] | no state change |
| "From + Pending Out" | S.N. [2] | no state change |
| "Both" | S.N. [2] | no state change |
+------------------------------------------------------------------+
[1] If the user previously sent presence of type "subscribed" as
described under Appendix A.2.3, then the server MAY auto-reply with
"subscribed" and change the state to "From" rather than "None +
Pending In".
[2] Server SHOULD auto-reply with "subscribed".
A.3.2. Unsubscribe
When the user's server receives a presence stanza of type
"unsubscribe" for the user from the contact, if the stanza results in
a subscription state change from the user's perspective then the
user's server MUST change the state, MUST deliver the presence stanza
from the contact to the user, and SHOULD auto-reply by sending a
presence stanza of type "unsubscribed" to the contact on behalf of
the user. Otherwise the user's server MUST NOT change the state and
(because there is no stage change) SHOULD NOT deliver the stanza.
These rules are summarized in the following table.
Saint-Andre Expires October 2, 2010 [Page 95]

Internet-Draft XMPP IM March 2010
Table 6: Processing of inbound "unsubscribe" stanzas
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
| "None" | S.N. | no state change |
| "None + Pending Out" | S.N. | no state change |
| "None + Pending In" | MUST [1] | "None" |
| "None + Pending Out+In" | MUST [1] | "None + Pending Out" |
| "To" | S.N. | no state change |
| "To + Pending In" | MUST [1] | "To" |
| "From" | MUST [1] | "None" |
| "From + Pending Out" | MUST [1] | "None + Pending Out |
| "Both" | MUST [1] | "To" |
+------------------------------------------------------------------+
[1] Server SHOULD auto-reply with "unsubscribed".
A.3.3. Subscribed
When the user's server receives a presence stanza of type
"subscribed" for the user from the contact, if there is no pending
outbound request for access to the contact's presence information,
then it MUST NOT change the subscription state and (because there is
no state change) SHOULD NOT deliver the stanza to the user. If there
is a pending outbound request for access to the contact's presence
information and the inbound presence stanza of type "subscribed"
results in a subscription state change, then the user's server MUST
change the subscription state and MUST deliver the stanza to the
user. If the user already has access to the contact's presence
information, the inbound presence stanza of type "subscribed" does
not result in a subscription state change; therefore the user's
server MUST NOT change the subscription state and (because there is
no state change) SHOULD NOT deliver the stanza to the user. These
rules are summarized in the following table.
Saint-Andre Expires October 2, 2010 [Page 96]

Internet-Draft XMPP IM March 2010Appendix B. Blocking Communication
Sections 2.3.5 and 5.4.10 of [IMP-REQS] require that a compliant
instant messaging and presence technology must enable a user to block
communications from selected users. Protocols for doing so are
specified in [XEP-0016] and [XEP-0191].
Appendix C. vCards
Sections 3.1.3 and 4.1.4 of [IMP-REQS] require that it be possible to
retrieve out-of-band contact information for other users (e.g.,
telephone number or email address). An XML representation of the
vCard specification defined in RFC 2426 [VCARD] is in common use
within the Jabber community to provide such information but is out of
scope for this specification (documentation of this protocol is
contained in [XEP-0054]).
Appendix D. XML Schemas
Because validation of XML streams and stanzas is optional, the
following XML schemas are provided for descriptive purposes only.
These schemas are not normative.
The following schemas formally define various XML namespaces used in
the core XMPP protocols, in conformance with [XML-SCHEMA]. For
schemas defining namespaces for XML streams and other core aspects of
XMPP, refer to [XMPP-CORE].
D.1. jabber:client
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='jabber:client'
xmlns='jabber:client'
elementFormDefault='qualified'>
<xs:import
namespace='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<xs:element name='message'>
<xs:complexType>
<xs:sequence>
<xs:choice minOccurs='0' maxOccurs='unbounded'>
<xs:element ref='subject'/>
Saint-Andre Expires October 2, 2010 [Page 98]

Internet-Draft XMPP IM March 2010
substantive modifications were made from RFC 3921.
o The protocol for session establishment was determined to be
unnecessary and therefore the content previously defined in
Section 3 of RFC 3921 was removed. However, for the sake of
backward-compatibility server implementations are encouraged to
advertise support for the feature, even though session
establishment is a "no-op".
o In order to more seamlessly repair lack of synchronization in
subscription states between rosters located at different servers,
clarified and modified error handling related to presence
subscription requests, presence probes and presence notifications.
o Explicitly specified that a server is allowed to deliver a message
stanza of type "chat" or "normal" to all resources.
o Added optional versioning of roster information to save bandwidth
in cases where the roster has not changed (or has changed very
little) between sessions; the relevant protocol interactions were
originally described in [XEP-0237].
o Added optional server support for pre-approved presence
subscriptions via presence stanzas of type "subscribed" and the
optional "subscribed" value for the 'ask' flag.
o Added optional 'parent' attribute to <thread/> element
o Moved the protocol for communications blocking (specified in
Section 10 of RFC 3921) back to [XEP-0016], from which it was
originally taken.
In addition, numerous changes of an editorial nature were made in
order to more fully specify and clearly explain the protocols,
including the following.
o Recommended returning presence unavailable in response to probes.
o Clarified handling of presence probes sent to full JIDs.
o Explicitly specified that the default value for the presence
<priority/> element is zero.
Appendix F. Copying Conditions
Regarding this entire document or any portion of it, the author makes
no guarantees and is not responsible for any damage resulting from
its use. The author grants irrevocable permission to anyone to use,
modify, and distribute it in any way that does not diminish the
rights of anyone else to use, modify, and distribute it, provided
that redistributed derivative works do not contain misleading author
or version information. Derivative works need not be licensed under
similar terms.
Saint-Andre Expires October 2, 2010 [Page 109]